GMforPowergamers
Legend
I have to agree with Max... but with a bit of a different solution... if you front load those changes you MAY be able to pull it off...I disagree. If the DM is changing 1 monster out of 8, metagaming is very much incentivized because it's still far superior to have advantage in 7 fights than it is to maybe have bad luck in the 8th.
If you aren't changing most of the monsters, it's still superior to have an advantage in most of the fights.
game 1- all normal monsters, game 2- 3 normal fights 1 homebrew swap, game 3- all homebrew swap, game 4- 3 homebrew swap 1 normal, game 5- all normal monsters, game 6- 2 normal 2 homebrew
that is if we average 4 fights a night 24 fights 10 of them homebrew... even if your next 5 games are all normal monsters you may have them 'worried' enough... or if you throw 1 in 8 after that you would 'keep them on there toes'