Would this require a change in the BCH protocol?
As far as I know... transactions with multiple OP_RETURNs in one transaction are considered "non-standard" by miners and are not relayed at present... would thus need to do multiple..
The protocol doesn't prohibit it. A miner could mine a transaction with more than 1 provably unspendable output. The issue is the nodes consider them nonstandard and won't relay them.
