We have to move our toilet drain which was y'd into the main drain, but was installed improperly for code and interferes with shower placement. We want to cut the drain back and then put in a 90 degree piece in order to move the toilet/ drain over to a more appropriate distance from the shower. Can you put in a 90 degree piece and still have efficient or tolerable drainage from a toilet?

Can you put in a 90 degree piece and still have efficient or tolerable drainage from a toilet?
Not a 90 but a long sweep,(see image)will give you better drainage providing you can maintain 1/4" per foot slope. Good luck. Tom