My point is that talking about immutability of a blockchain in this kind of case doesn't make sense. The technical immutability is preserved, and on the level of token amounts the concept of immutability doesn't apply because everything is done by the rules.

If an account is a multisig account, like every account is in EOS, then everyone who has the keys to the account has an ability to do transactions.

So rather than speaking about "immutability", we should be speaking how to make the system fair, transparent, etc. so that all parties can trust it.