I picked my breed offsets by looking through this directory (
P.O.N.D.) for ones not in use. Originally, I was rather random in my selection (sorta choosing "D7" beginnings), but lately (starting with my hamster), I've been using numbers that end in "05" and have not been listed in the directory.
If a breed clashes with another one you have, please use an overwriting file instead (if one doesn't exist, I can make one).