I was thinking of using a few on some of my non-vis pets and the message at the bottom of the genetic mutator info blurb says that a pet can only be affected by one once...am I right in reading that as if I use a mutator on a pet, I am then stuck with the outcome and can't use another to try to get a prettier gene?

Once a genetic mutator (lesser or greater) has been used on a pet, you can't use another one on it. In the case of the lesser mutators, you don't get to choose what the pet gets, it will either be a vis or a carry. For greater mutators, you get to choose the trait the pet gets. ^^

Thank you. Guess I am saving up a whole bunch of gold then, I don't want to risk favorite pets with random chance.