I'm curious your reasoning on this. I'm 100% okay with the breeder choosing the registered name (I would prefer the freedom to come up with one but I don't mind one already being in place) but I would never buy a dog I couldn't choose the call name for. I know you said they *can* change it, but why do you prefer they keep it?
Because the call names the puppies are given generally tie into the registered names, is all. In the end it really doesn't matter what the owner actually calls the puppy, because we triple register our puppies with all of the registries we compete in, and give them separate names that essentially do the same thing. So for example, these are the names for our current "horror film" litter of five puppies.

It's really just icing if the owner decides to keep the call name we've been using.