Ideally when replacing the BB one will check on the amount of clearance between the chain stay and the inner chain ring before removing the BB. If that gap was less than a few MMs I would be very careful about installing a shorter BB axle as the ring might contact the frame under pedaling loads. If the gap was fairly large then the concerns about clearance are less. The same goes with how much travel the ft der has. if the resulting chainline is different one wants the ft der to be able to be adjusted to this new range of travel and not "bottom out" on either its limit screws or against the side of the seat tube.

Generally changing the front chain line by a Mm or 2 is not a big deal WRT the chain running or with shifting as long as the system is checked and readjusted as needed. Andy