You're welcome @carlosmertens - you only need to register them once unless you move them to another wallet, in that case you'd need to register them again (as the new wallet would have a different Ethereum public address to the one you were using).

As long as the Ethereum public address of the wallet you're using to store the EOS tokens is mapped to the EOS public address which you would have generated and for which you only hold the private key, then you should be fine once the ICO has ended.