I think what he meant was for it to be something you purchased once from the shop, and from that point on for a cost in temporary stats (such as AP, VP, VE, or EXP) you could change its name, with a cooldown for each individual creature of one month, or some other time frame.
I don't know how hard that would be to code, however.
I think a more logical version would be to have say 5 name change tokens in the shop, that when purchased gave you a non-transferable (or possibly even transferable) token, which so long as the game detected you as having at least one you where able to change a creatures name. Although, that said, once again I don't know how easy that would be to code, and I think it would make more sense for the tokens to only be usable, and hence consumed, on creatures that are already at their maximum level (and hence can't have their name changed by any other method)