DS never had an issue with changing but some babies have a reaction I would say I think if u want to use a certain one u have to take it with u to the hospital I reckon I would rather do that anyway my hospital u had to provide formula if u want to use it from the start
I took formula to the hospital when I had DD1 because I knew I was going to formula feed her from the start. The hospital had no issue with it.

As for changing formulas, I've just changed over to another one, and given the new formula a try for a week or something (so usually the tin) to see how it goes with them.