I did my PhD in a yeast DNA repair and mutagenesis lab. I'm pretty sure that copper in and of itself is not mutagenic. Some copper complexes, sure, but I don't think copper ions are (at least not directly that I know of).
Even if it did cause mutations, unless the mutation was advantageous, the rest of the culture would presumably out-compete the mutant yeast just based on shear number of cells. Maybe you would notice something with serial repitching, but I wouldn't really worry about this.
If using a little bit of copper (say in chilling) released enough copper ions into wort to be cytotoxic to yeast, I wouldn't be drinking beer.