I don't fully understand your question. If you send your funds to the new address, your bitcoin will be in the new address on the blockchain. However, you can still use your old address will still be valid and bitcoin can be sent to your old address. Bitcoin wallwt address does not expire but it's good not to reuse one same address to receive bitcoin.
So there would be two address to use? I though the old one (the one being changed) would be not usable afterward..