Getting the tuning on a four isn't a problem- might need a truss rod tweak and intonation adjustment, but that's not a big job. What is a problem is trying to use the same strings to tune up to standard- you would either have too much tension on the neck from the larger strings for tuning down, or standard strings which would be totally floppy if you tune them down to drop B.
Just to clarify, by drop B do you mean BF#BE?