Take back or no

If a beginner player is unaware of a rule, and because of this they are unaware of this rule they make a move they would not normally make, are they allowed to take that move back.

Ex: Player 1 puts player 2 is a position that would normally put them in a stalemate but player 2 has a pawn left so this is not the case. Player 1 takes player 2's last pawn and right after player 1 is told that that makes a stale mate. But here's the catch. If player 1 knew of this rule he had a pawn that in 2 moves, could have put player 2 into checkmate. Can player 1 take back their move and, instead of a stalemate, put player 2 into checkmate? 

I would only ask for a slip of finger, an obvious drop

There is a take back option on unrated daily games.

Had a player make an unsound sacrifice ...Rxh3, then claimed mouseslip. I allowed him to take the move back, and he proceeded to play ...Na6. That was one spectacular mouseslip!

No.  Play better next time having learned from the mistake.  That is how we learn after all.