Can you wear a combat patch for a unit you supported?

You can find AR 670-1 at this link...dated 31 March 2014, its on page 33
http://www.apd.army.mil/pdffiles/r670_1.pdf

Bottom Line: What ever the patch is of the unit you are assigned to, unless you have authorization from the DCS, G-1 or a designated representative to wear a different patch.

21–17. Shoulder sleeve insignia–former wartime service
a. General. Authorization to wear a SSI indicating FWTS applies only to Soldiers who are/were assigned to U.S. Army units that meet all the following criteria:
(1) The Secretary of the Army or higher must declare the theater or area of operation as a hostile environment to which the unit is assigned or Congress must pass a Declaration of War.
(2) The units must have actively participated in or supported ground combat operations against hostile forces in which they were exposed to the threat of enemy action or fire, either directly or indirectly.
(3) The military operation normally must have lasted for a period of 30 days or longer. An exception may be made when U.S. Army forces are engaged with a hostile force for a shorter period of time, when they meet all other criteria, and a recommendation from the general or flag officer in command is forwarded to the Chief of Staff, Army.
(4) The Chief of Staff, Army must approve the authorization for wearing the SSI for FWTS. Note: Units are not authorized to make modifications to their SSI, or SSI-FWTS without prior approval from the DCS, G-1. A mirror image SSI-FWTS is considered a modification.
(5) Personnel who served in a designated area as a civilian or a member of another Service, but were not a member of the U.S. Army during one of the specified periods are not authorized to wear the SSI-FWTS.
(6) Unless otherwise approved by this regulation, Soldiers attached or under operational control (OPCON) to other services are not authorized to wear their patches as their SSI-FWTS without written approval from DCS, G-1 or a designated representative.
(7) Soldiers of all Army components (Active, ARNG, and USAR) who deploy during periods of service designated for wear of the SSI-FWTS are authorized to wear a SSI-FWTS. There are no time-in-theater requirements for authorization to wear the SSI-FWTS. Soldiers may not earn more than one SSI-FWTS during the same deployment.
(a) A deployed unit (company or higher) will wear its unit SSI as the SSI-FWTS, regardless of the headquarters element deploying and the unit alignment or OPCON during the period of deployment.
(b) A deployed unit will not wear its assigned SSI as its SSI-FWTS when the SSI belongs to a major command, such as an ACOM/ASCC/DRU or State Area Command, or a non-deployable unit. In such cases, the unit will wear the SSI of the lowest echelon Army unit (company or higher) in the deployed chain of command as the SSI-FWTS. When
there is no intermediate unit (company or higher) in the deployed chain of command, these deployed Soldiers will wear the SSI of the senior command in the theater as its SSI-FWTS.
(c) When echelons below company level (such as teams or squads) deploy, members of these units will wear the SSI of the lowest echelon deployed Army unit (company or higher) in the deployed chain of command (based on written orders) as the SSI-FWTS. When there is no intermediate unit (company or higher) in the deployed chain of
command, these deployed Soldiers will wear the SSI of the senior command in the theater as its SSI-FWTS.
(d) Individual Soldiers who are attached (to include OPCON, cross-leveled, assigned, or augmenting deployed units) will wear the same SSI-FWTS worn by members of the deployed Army unit (company or higher) to which attached by written orders. A Soldier who is further attached (to one or more units) during one deployment will only wear the SSIFWTS for the first Army unit (company or higher) to which attached by written orders. Soldiers who deploy with their unit (company level or higher) will wear the SSI-FWTS as outlined in paragraph 21–17a(7)(a), regardless how many times they are further attached to other units as individuals or teams. Members of trial defense and Criminal
Investigation Division Command will wear the SSI of their respective commands as their SSI-FWTS.
b. Authorization. Authorization applies only to members of the Army who were assigned to the designated location overseas with U.S. Army organizations during the following periods:
(1) World War II: between 7 December 1941 and 2 September 1946, both dates inclusive. Soldiers who served with the USMC during World War II from 15 March 1943 through 2 September 1946 may wear the SSI-FWTS for the designated Marine Corps unit.
(2) Korea: between 27 June 1950 and 27 July 1954, both dates inclusive. Also between 1 April 1968 and 31 August 1973, for those personnel who were awarded the Purple Heart, combat infantryman badge, combat medical badge, or who qualified for at least one month of hostile fire pay for service in a hostile fire area in Korea.
(3) The Vietnam theater, including Thailand, Laos, and Cambodia: between 1 July 1958 and 28 March 1973, both dates inclusive.
(4) The Dominican Republic: between 29 April 1965 and 21 September 1966, both dates inclusive. Individuals are authorized to wear one of three organizational SSI: XVIII Airborne Corps, 82d Airborne Division, or 5th Logistical Command. Individuals previously attached, assigned, or under the OPCON of these units will wear their respective
insignia. A fourth organizational SSI (Office of Economic Adjustment–Spanish equivalent of Organization of American States) is authorized for individuals who were not in one of the three units listed above.
(5) Grenada, to include the Green and Carriacou Islands: between 24 October 1983 and 21 November 1983, both dates inclusive. Personnel are authorized to wear one of the following organizational SSI: XVIII Airborne Corps; 82d Airborne Division; 1st Special Operations Command (Airborne); 1st Corps Support Command; 20th Engineer Brigade;
35th Signal Brigade; 16th Military Police Brigade; 44th Medical Brigade; 1st Battalion (Ranger), 75th Ranger Regiment; 2d Battalion (Ranger), 75th Ranger Regiment; and 101st Airborne Division (Air Assault). Individuals attached to, or under the OPCON of these units will wear their respective organizational SSI. Individuals attached to, or under the OPCON of any unit whose parent organization is not authorized SSI, will wear the SSI of the unit to
which attached or the unit that had OPCON.
(6) Lebanon: between 6 August 1983 and 24 April 1984 for Soldiers assigned to the Field Artillery School Target Acquisition Battery or the 214th Field Artillery Brigade, who were attached to the U.S. Marine Corps forces in and around Beirut, Lebanon, for the purpose of counterfire support.
(7) Korea: 23 November 1984, for Soldiers who participated directly in the firefight with North Korean guards at the Joint Security Area, Panmunjom, Korea.
(8) Persian Gulf: between 27 July 1987 and 1 August 1990 for Soldiers assigned or attached to, or under the OPCON of, a unit whose mission was direct support to Operation Earnest Will. Soldiers must have been eligible for the Armed Forces Expeditionary Medal and imminent danger pay.
(9) Panama: between 20 December 1989 and 31 January 1990 for Soldiers assigned to the following units who participated in Operation Just Cause: XVIII Airborne Corps; U.S. Army Special Operations Command; U.S. Army South; 7th Infantry Division (Light); 82d Airborne Division; 5th Infantry Division (M); 1st Special Operations Command; 193d Infantry Brigade; 1st Corps Support Command; 16th Military Police Brigade; 18th Aviation Brigade;
35th Signal Brigade; 7th Special Forces Group; 75th Ranger Regiment; 1st , 2d, and 3d Battalions, 75th Ranger Regiment; 470th Military Intelligence Brigade; 525th Military Intelligence Brigade; 44th Medical Brigade; 1109th Signal Brigade; Military Surface Deployment and Distribution Command; and Criminal Investigation Command.
Soldiers assigned to units not listed above will wear the SSI of the unit to which attached or the unit that had OPCON. Soldiers assigned to units not listed above and not attached to, or under the OPCON of any of the units listed above, will wear the SSI of the U.S. Army South.
(10) The Persian Gulf: between 17 January 1991 and 31 August 1993, both dates inclusive, for Soldiers participating in Operation Desert Storm. Soldiers must have been assigned or attached to, or under the OPCON of, a unit whose mission was direct support to Operation Desert Storm; they must have received imminent danger pay and had been under the command and control of U.S. Army Element U.S. Central Command.
(11) El Salvador: between 1 January 1981 and 1 February 1992, both dates inclusive, for those personnel who participated in El Salvador operations.
(12) Somalia: between 5 December 1992 and 31 March 1995, both dates inclusive, for Soldiers who participated in Operation Restore Hope/Continue Hope/United Shield. Additionally, Soldiers assigned to Joint Task Forces Patriot Defender, Elusive Concept, and Proven Force are authorized to wear SSI–FWTS even though they were not under the
command and control of the U.S. Army Element of U.S. Central Command.
(13) Operation Enduring Freedom (OEF): between 19 September 2001 and a date to be determined, for Soldiers assigned to Afghanistan, Pakistan, Tajikistan, Turkmenistan, and Uzbekistan; Between 9 January 2002 and a date to be determined for those Soldiers assigned to the Philippines, in support of Operation Enduring Freedom, who were
receiving combat zone tax exclusion and imminent danger pay (IDP), and who meet the criteria of paragraph 21–17a. Between 31 July 2002 and a date to be determined, for Soldiers deployed to the U.S. Central Command (CENTCOM) as identified by CENTCOM Command Center–Joint Staff for Personnel and Administration. Soldiers who were
deployed in the area of operations on training exercises or in support of operations other than OEF are not authorized the SSI–FWTS, unless those exercises or operations became combat or support missions to OEF.
(14) Operation Iraqi Freedom (OIF): between 19 March 2003 to 31 August 2010, for Soldiers assigned to units participating in OIF. Soldiers must have been deployed in the CENTCOM area of operations, or participated in OIF while deployed in Turkey, Israel, or on Aegis cruisers. Soldiers who served with the 1st Marine Division between 19 March 2003 and 21 April 2003 during combat operations in support of OIF are authorized to wear the 1st Marine Division SSI as their SSI–FWTS. Soldiers who were deployed in the area of operations on training exercises or in support of operations other than OIF not authorized the SSI-FWTS, unless those exercises or operations became combat or support missions to OIF.
(15) Operation New Dawn (OND): between 1 September 2010 and 31 December 2011 for Soldiers assigned to units participating in support of OND. Soldiers must have been deployed in the CENTCOM area of operations or participated in OND while deployed in Turkey, Israel, or on Aegis cruisers. Soldiers who were deployed in the area of
operations on training exercises or in support of operations other than OND are not authorized the SSI-FWTS, unless those exercises or operations became combat or support missions to OND.
(16) Future Operations: Combatants Commanders may request wear of the SSI-FWTS for future areas of operation designated and approved by the Secretary of the Army.

The patch you wore over is the one you keep unless you were assigned to a different unit, or your company or platoon was attached to someone else. In that case you will have attachment orders authorizing you to wear the other patch.

The clarification came out in an ALARACT message a few years ago after everyone and their mom decided they were authorized to wear a JSOC/SFG/USASOC/Ranger combat patch since they supported them once on a mission.

7 patches later who cares lol