Made a quick macro which adds the command /rr to rename your currently summoned pet,
Code:
/script SLASH_RR1 = "/rr" SlashCmdList["RR"] = function(msg, edit) C_PetJournal.SetCustomName(C_PetJournal.GetSummonedPetID(), string.sub(msg, 0, 16)) end
To use it, just type: /rr wang and your pet will be renamed to wang. Handy if you want to make a couple of macros to point at your pet and insult the other faction.
You can rename your pet quite a few times but it does take a second to update after setting it.
Good idea OP.