You cannnot override the machine. There is NO POSSIBLE WAY to ring up alcohol before 12 on Sunday (in Texas).
Funny story though . . . I had a guy come up at 11:55 one Sunday with a bottle of wine and the makings for spaghetti and garlic toast . . . he was so cool about it:
Customer: *checks REGISTER'S time (instead of his own watch . . . yay!)* Aww, man, 5 minutes!
Me: I'll ring your stuff up slowly . . .
C: *chuckles* Okay. *watches clock the whole time . . . watches me finish before 12* Oh no, I don't mean to hold everybody up . . .
M: Yeah, I'm sorry, I wish I could manually do it . . .
Pretty soon my whole line (4 people in great moods, I might add
) was watching the register's clock for noon. It was just so amusing and a funny way to start my shift!