Hussar
Legend
Regardless of how new the players are, if you agree to play game X and then don't use the rules for game X, you're breaking the contract.
New players may not have the experience necessary to tell that you're being fraudulent, but a contract break is not dependent on detection.
I think the question becomes, how important is that social contract?
We've been conditioned to think of the social contract as being very much a two way street, but, it wasn't always this way. In earlier D&D, for example, the DM was very much empowered to change rules at will and the players were strongly advised to simply trust their DM and roll with it.
Now, I'm not sure I'd personally want to go back to that, but, then again, it would be hard for me to come into an RPG without bringing in all my history and baggage as well. But, a new player simply doesn't have the background to be able to judge what is "good" or "bad" beyond whether or not the current play is fun.
If the players are having fun, and the DM is having fun, the social contract can go hang.