Switching difficulty at Bioshock.

I was just wondering if it is possible to play the whole game on Hard difficulty without using a Vita-Chamber and at the very end where you need to help the little sister before killing Fountain can switch to Survivor difficulty to get the two Survivor trophies.

Is that possible?

no i dont think so,

it tells you in the menu doesnt it?

like changing the settings may affect trophies

It is not possible. You have to complete the game from start to end without changing the level; hard or survivor in order to get trophies for the level you completed it at.