fog stays, you don't need a para...
like i said THERE IS A BUTTON IN EVENT COMMANDS CALLED "CHANGE MAP SETTINGS"
may just maybe, the 2nd option, and i am only guessing, is change fog
and if that is so, maybe just maybe, to cancel the fog out you possibly need to remove the fog like you got it in...
but that's just me guessing...
also if you don't want to use events, you can copy paste the same tileset, making one with fog and one without...
(please don't say "omg where button show pictures to me" ... ~_~)