Is there any risk, if some people run old wallets and make some transactions to bypass this ban?
Anyone running the old client will essentially be on their own network (or blockchain fork.. i prefer to consider it their own network). In that network they will be exposed to the scam premine as it will be able to move around, if the original dev decides to do so.
People running the new patched client (v1.8.2) including myself and anyone testing it right now.. are on the right network/blockchain fork.. and are essentially inoculated against the premine.. and hopefully that will be all exchanges/pools.