Ok you have this really bad habit of declaring people wrong without either backing up what you are saying or even understanding what they saying. It doesn't matter what all GM positions have or do, what matters is if the Texans GM position has more authority than whatever he is doing for the Pats. If it does then this is considered a promotion and, assuming the league follows its own rules, the Pats can't stop it. If it doesn't then its considered a lateral move and they can stop it. The problem the Pats have is, despite what some on here think, for the Texans the Gm does indeed seem to have final say on who is drafted and such but for the Pats Belichick has final say.
All this has been discussed in detail with links to not just reports but the NFL rules themselves in all their legalese glory on the message board. So rather than being in a hurry to declare everyone wrong your second day here why don't you catch up on what has been said.