I'll just move btc after the split to a new address and then export the keys of the then empty btc addresses.
Remember to empty your entire Armory wallet of BTC before you export private keys to something less secure. I am 95% sure that if somebody gets two private keys from the Armory chain, then he has them all. And if somebody has just one private key, and the chaincode
which is unencrypted in the watch-only wallet, then all following private keys are compromized.