In theory, if you validate on the chain that Vitalik doesn't like, he will destroy your 32ETH on the good-boy Vitalik chain.
How will he know I validate ETH-new's chain? I can spend on both chains, and I'm sure he would be fine by the assumption that I'm selling the ETH-new he disapproves of, to buy his ETH-old. But, you can't know with certainty that an ETH-old staker uses the same funds to stake ETH-new. Say, for example, that I mixed ETH-new, and then staked those.
True; mixing and putting the coins back in for the same amount of stake should work. I think the slashing mechanic only works if you just don't move the funds and keep them on both chains, verifying on both of them.
There's no identity or KYC (god forbid) attached to your stake, soo you could most definitely sell the new-ETH, buy them again (or mix them) and acquire the same amount of stake on both chains.