Can a character of discharge from the USMC be changed from General to Honorable?

Agree with SSG Rogerson, every service branch has the same procedure.

Yes it is. You need to file a case with the Board of Corrections of Military Records. Get yourself a lawyer in Washington D.C. that does that kind of case. You need to gather all your paper work to document why you missed the formation. That the Marine Corps gave you a general discharge is not untypical. They tend to be petty, revengeful and draconian at times in handing out bad Reenlistment codes and discharges for minor offenses. You probably pissed off a Senior NCO or Company Grade officer and they were out for revenge and one who wanted to screw you over. I've seen them hand out and do such things for refusal to reenlist with NO NJP or other negatives. But you can get the general undone and upgraded to an honorable discharge if there was no other offenses. Why they gave you a General with only one NJP is beyond me but it is what it is. Just have your ducks in a row and all the documentation you can get and even get some character references. Good luck.

Nobody is downgraded from Honorable to General Discharge for being late once.

Someone help me out here, but character of discharge was well above, and outside of the chain of command, and the chain of command had very little influence to downgrade it. As a Company Commander and as a Battalion Commander, I was never successful in getting a discharge downgraded, and there were three deadbeats I asked for it to happen.

I hate to be the bearer of bad news but, yes, it is possible; however, it is very unlikely. Contrary to barracks rumint the percentages of character of discharge changes are extremely low...like less than 1% low... I agree with most comments here, there's probably more to this story than we're hearing...

You can follow processes for your concerns to undergo a Discharge Review Board. Here are a few helpful links. I recommend that you reach out to either your local veteran service rganization (vso), congressional representative's veteran liason, current or retired JAG officer, or a veterans' legal advocacy group (even a student group at a law school) to request assistance in preparing your documents.

https://www.military.com/benefits/records-and-forms/discharge-review.html/amp

https://www.public.navy.mil/bupers-npc/career/recordsmanagement/Pages/BCNR.aspx

In my opinion the military usually gets these right, however hopefully for those few vets out there that need this info, you find this helpful.

12/9/2020 Update to original post- The VA Now provides customized instructions in many cases, please see https://www.va.gov/discharge-upgrade-instructions/

If you were being separated prior to your contract completion due to injury, your discharge would be a general "under honorable" regardless. You only get an Honorable discharge If you reach the end of your contract, otherwise, It's a general under honorable discharge. If they made that change, it was because they were going to let you EAS, but then decided to Adsep you instead, in which case that change would have to be made. Also, a General Under Honorable conditions discharge doesn't affect your GI Bill or any other benefits. Other than Honorable, Bad Conduct, and certainly, Dishonorable discharges cause you to lose benefits. A General under Honorable discharge simply means you were discharged honorably before finishing that current contract. So, that is an honorable discharge and you can use your GI Bill or Voc Rehab.

That's up to the USMC review board. You can submit your request for review and change. Be mindful of the fact that your record(s) will be carefully reviewed by the board. If the record supports the characterization, it will stand.
Seems as though it's only become an issue because you want to use the GI Bill.
I think something's missing from your story. Submit your request for review together with your evidence. It's been 11 years - you're running out of time.
"If your service ended before January 1, 2013, your Post-9/11 GI Bill (Chapter 33) benefits will expire 15 years after your last separation date from active service. You must use all of your benefits by that time or you'll lose whatever's left."

Having seen countless packages for discharge, one NJP did not get you a GUH. If it did, you have grounds for appeal to the BCNR. But given how high up a determination package goes and how often it gets reviewed, ie by Senior Enlisted and Bn/Regt XOs, that was not your only documented issue.

The reason you got a general under less than honorable isn't just because of that, my guess is you've been in trouble more than once. I knew guys who got in trouble for being UA, didn't get a court martial, had it handled the way yours was, NJP, and still got an honorable discharge because it was the one and only time they were in trouble, plus had high Pro and Con marks the entire time they were active duty, so the low set after NJP didn't bring their average down enough. You're probably to late to have a review board look at it now, its been 11 years. You reap what you sow in life