A bitcoin node still downloads and validates all transactions and blocks, even if pruning is enabled. And if you set up your node to track your wallet history, it will store those transactions even if they're past the prune period.

Op_returns are provably unspendable thus, pruneable. If it’s in a block you have to accept it or you’re out of sync with the rest of the network. To win your war you need to fork bitcoin. Or you can just ignore it and let your node prune it.

No, a pruned node verifies everything, no matter how far back it is.