From Ivo : About Private Key Change -

"If you generate a new address on your wallet, use the converter to convert to old style address and send the coins.
If you reuse an old address that was already in your wallet before you upgraded, you can still send the coins there and they will show up..


The thing to remember is that the private keys remain the same, just the way the public address is shown changed

So if the private key is in your wallet.dat ; you are fine"