What is likely to be the punishment for a soldier who altered their profile?

@SPC james Davison He will be lucky if it is referred to a courts martial. That would be under fraud to alter a service record. I would suspect at very minimum he would lose a rank and get a whopper fine. When I was in the Corps a 1stSgt was brought up on charges for doing that. He got busted to a Gunnery Sergeant for it. He retired shortly there after.

IT depends on how lenient or strict the commander is. If they are lenient it could be as light as a GOMAR. It gets progressively worse from there. He lied, he forged a document that is official and technically he is malingering. His commander will likely not push for a Court Martial but certain could Article 15 him and in this instance it not be a summarized but a Field grade so he loses rank, pay, confinement and extra duty. And most likely he gets flagged for re-enlistment.

Funny it’s alright for anyone to do it in office working with 1SG and Captain or S shops. See it every PT test for points or weight. But a soldier in normal ranks will probably get counseling or if upper ranks want to make an example or don’t like the Soldier give an Article 15.

UCMJ...Article 15. He "never was a bad soldier"? He lied and falsified documentation. That's a "bad" soldier!

Our CSM in front of the unit did halfway push-ups during his PT test and everyone didn't question it. Yet, we all laughed at each other when we did the PT test saying hey, don't do Sgt major Pushups! Go all the way down and then lock out your elbows all the way up, your not a CSM over this unit! He(CSM) got highest PT score that day. Situps too we're questionable, elbows up counted as a sit-up only for our CSM. Probably got an award for it too and a bonus.

Gee, seeing that an official document was altered, UCMJ Article 123 and federal actions
18 U.S. Code § 1028 - Fraud and related activity in connection with identification documents, authentication features, and information.

I do not believe a SPC and below will get that harsh of a sentence, but the severity needs to be enforced.
I would seek Article 15 reduction.

When I was serving back in 1967 you did that it’s jail time.

Did he alter it so he could return to duty or alter it to get out of duty?

Probably an article 15; so rank, pay, and time.

Just like any official document. If an individual alters or amends a document without approval or authority is guilty of forgery. Only person that can alter such document is the issuer. The level of punishment all depends on the severity of the altered document. It may be a NJP or a CM procedure.
I give you an example when I was in the Navy, we have LOG BOOKS for Watch Standards have to fill in when visiting a certain area. But some has been caught filling out the whole watch on the 1st visit which we called it "Gun Decking". They got NJP with restriction/extra duty, loss of pay and or rank reduction along with restriction/extra duty, loss of pay. None went to the CM level.