My question involves criminal law for the state of: Texas

Hi, My boyfriend was arrested in Texas at a Private Prison he worked at for possession of marijuana. He was not aware of any marijuana in his car, which is why he consented to the search. They asked if they could search and he said yes. That's not the issue. He was arrested and charged with a Class B misdemeanor. He hired a lawyer and has been in and out of court. He took a drug test the day he got out of jail, and a lie detector test which they gave him three times and he passed all three times. He just went to court again and after his Lawyer talked to the DA and judge, they said they will not be dropping it and said if they go to court they may charge him with a felony with it being at a prison, and they are doing him a favor. His lawyer is pretty much telling him to just take the charge, I don't see why it wouldn't be dropped to a class c, I have researched and found alot of cases where this happened, but what do I know. Plus it is at a prison, but that is not what he is originally charged with.

My question is, how likely is it that this could be dropped to a class c misdemeanor of possession of drug paraphernalia, since this is his first and only criminal offense.

And can they after only arresting him for a class b, later change it a higher charge since it was at a prison?