What would happen if you took the source modified out the fixes, created 2 different wallet without the fix. You then send the money from the premine account through the modded wallet, to the wallet of the other account with the modded wallet. What would that do? Would that effectively transfer the coins from the premine to another account, thus it would be valid from there right?
Or do the nodes reject it? The nodes reject right?
Adding to what Maxikosw quoted from me:
That's why need to make sure that exchanges have the correct wallet, and that everyone updates to the new version so that they will not accept any coins sent from the banned address of the original developer. This way whoever remains in the old wallet could be sent those invalid coins (this creates a fork), but the network that people who use the updated wallet and exchanges are on will not accept any blocks that there is a transaction from the banned address, therefore we're safe.
It's the same for any other cryptocurrency, you can take the source and ban any address but it will not matter as the places that matter (exchanges and pools in the case of PoW coins) are on the correct blockchain running the correct wallet.