make sure you use gas every so often as the ethonal will clean everything and leave deposits and start to turn injectors black. the gas will clean all that up.
as far as switching between fuels. from what I've seen (I've seen a few tunners tune e85). they always run the gas as low as possible then add e85. that's how they tune it.
anywho when I switch fuels I keep an eye on knock sensor, make sure it doesn't knock when I switch maps.