But he can send the alls coins to the order addresss, to the other pc with the old version wallet, and he can change the original address...... its very easy.... I dont know... I think its not the solutions.
Doing so will cause immediate fork: new wallets will not accept a block that has that transaction. The code does if nheight > 18013 any attempt at transaction usign old address from either new or old wallet past that block will be rejected by ALL new wallets. Protection is on incoming AcceptBlock/processblock of clients.
In essence, even if he sends coins to old wallet running old code that can do the send.. newer clients will reject it, and be automatically on a different fork.