if your petz aren't getting along, and you'd like them to be friends, there's actually a (relatively) simple way to fix that!
first, open the disliked pet's file in a hex editor. scroll down past the zero bytes below the pet's breedfile, and you'll find a string of bytes like this, just before the pf magic text. this is the pet's GUID! record it for the next step.
now, open the other pet's file, and search for the GUID. we want to find the GUID in the affinity descriptor section of the association matrix, so you'll want the last instance of it in the file, since it's towards the bottom.
after the GUID, the next byte should be 00, which corresponds to "enemy". in catz, you want to change this to 02. in dogz, change it to 03. these correspond to a "buddy" relationship (which can become romantic if the petz can mate.) in dogz, 02 seems to be a "lower" buddy relationship (acquaintances?) you can also change this to 01, if you'd like them to have a neutral relationship. (for other types of relationship changes, simply change this byte from whatever its value is to whatever the value for the relationship type you want is.)
if the petz mutually dislike each other, you may need to repeat this process for the other pet as well!
after making any changes, be sure to run the pet file through PetzByte to recalculate the checksum.
if all has gone well, the petz should now be getting along just fine!