I dont know what that means.
It means if we didn’t have kohanim we would do piyon haben either. It’s just another example of a mitzvah which they didn’t keep, not because it was before matan Torah, but because it was a physical impossibility.
But those are very far fetched. Though arguably guess these mitzvahs fall into the category of “where the ability to do the mitzvah isn’t there”
Right. I don’t know why you think it’s far-fetched. They kept shechitah, ate matzah on Pesach, and even eruv Tavshilin. They only didn’t keep things which were impossibile to keep in the literal sense, or in cases where a different cheshbon took priority over the mitzvos which were considered only eino metzuveh (e.g. Yaakov Avinu marrying two sisters).