How yould you describe someone who is Ranger-tabbed, versus serving in one of the ranger regiments?

The U.S. Army Ranger Association is the oldest organization currently in existence that supports members of the Ranger community regardless of the conflict in which they served or the unit to which they were assigned. The Association has been asked to weigh in on the question of who qualifies to use the title U.S. Army Ranger. Those who study Ranger history will know that this until-now good natured barracks debate has flared in one form or another for at least seventy years. The short answer to this question is that anyone who graduated from the U.S. Army's Ranger School or who served in a Ranger-designated unit qualifies. These qualifications have been enshrined, albeit in a bit more detail, within our bylaws for decades and are consistent with the stance taken by the Department of the Army.

https://members.ranger.org/Who-Is-A-Ranger

“There is no official U.S. Army policy regarding the use of the term ‘Ranger,’” said Lt. Col. Ramirez, the spokesman with the Army’s Office of the Chief of Public Affairs, adding that “The designation ‘Ranger’ has been associated with Soldiers who either graduated from Ranger School or are assigned to the 75th Ranger Regiment.”

https://taskandpurpose.com/news/army-ranger-school-policy-unknown/

Bottom line, anyone who served in a Ranger unit or graduated from Ranger School can be called a Ranger.

If you were ever in the Regiment, or worked near them, you would have often heard "the tab is a school, the scroll is a way of life," implying that in contrast to those who did it for 70 days, they do it every day as a job.

In the context of any Infantry officer in any Infantry Bn, they would all be Ranger School graduates, and it would be redundant to mention that they completed Ranger school.
If they are any other basic or special branch in an Infantry Bn, I suppose it would be worth pointing it out if that experience was also germane to the topic.

Rangers appreciate that you seek to say this right. I suggest the following: "with one of my colleagues, a Ranger-qualified Officer in an Infantry battalion down the road, admitting to me..."