as a coach it should be said that you only should change someones grip if its going to help alot, something must be not ideal for a drastic change of grip.
I regards to the BH grip it needs to be changed to give you a stronger wrist position
I regards to the serve, i would hazard a guess that you are changing from a FH grip to a conti. Don't worry, everybody who ever played tennis has had difficulty with this grip change, but once you get it it helps your serve infinite. The conti grip allows for much better wrist flexion and better shoulder rotation (so long as the ball toss is adjusted to suit). It should also allow you to hit all 3 types of serve from the one grip.
but as the old saying goes...practice practice practice