It will update itself on the Rewards program, however it won't be instant.
Will I still receive Xbox LIVE Rewards Points if I change my Windows Live ID (email)?
A. Yes. If you migrate your Xbox LIVE Rewards account to a new Windows Live ID (email), there may be up to a 96 hour delay before you can log into Xbox LIVE Rewards with your new email. You may even be prompted to re-register – just ignore this request,
but it will not hurt if you re-register. If you attempt to log in with your new email but Xbox LIVE Rewards does not recognize you, you can always check on your points using your old email. Rest assured, once the migration is complete, your points will be
moved, and you will be able to access the information with your newly linked email.
Did this solve your problem?
Sorry this didn't help.
Great! Thanks for marking this as the answer.
How satisfied are you with this reply?
Thanks for your feedback, it helps us improve the site.