Biology,
In answer to your first question. If the person admits that a takanos Chazal are binding but argues that he/she will not do it because he/she finds it offensive. That would not be apikorsus or meenus.
I have never heard of the Ran you are referring to so I cannot really comment. But it is true that the Rambam clearly holds that bizui Talmidei Chachamim is not apikorsus.
I also don’t know if bizui talmidei chachamim is limited to living talmidei chachamim or includes the non-living as well. I would have a hard time imagining imagining that not listening to talmidei chachamim, in and of itself, would constitute bizui.