rejecting transactions for using the "isvalid" validity bypass trick is not censorship. bitcoin is made with many rules. there is reasons why someone broadcasting a [insert shitcoin] tx on the bitcoin network wont see it in the block. because there are rules to reject transaction it does not understand.(well there used to be)
And who is going to do it? One pool rejects it and another confirms it.
If you run a node, or you mine, you can reject what you want, but if someone else wants it to go through, he can.
learn consensus. (where node majority agree on a rule causing the network to comply to that rule). then realise bitcoin is code and codes create rules. learn if core(node majority reference client) decides to code a rule that is enforced via consensus, everyone then follows.. especially when those sponsoring core then do a NYA mandatory upgrade to force complience by economic nodes and pools to speed up the consensus activation(as they have done before)
yes it can be done. but requires CORE to fix their mistakes, individuals editing their node get treated as opposition/threat to the core roadmap.