Note that your LiveID and your email address are usually the same, but they do not have to be. Your subscription ID is the LiveID you used to activate with originally. That LiveID is still valid, even if your email address has changed. You can change the alternate email address for your LiveID at http://account.live.com and renew your OneCare subscription using that LiveID at http://billing.microsoft.com
If you choose to get a new subscription using a new LiveID based on your new email address, you will need to reinstall OneCare.
-steve