" If any of the primary addresses for this policy are populated in the gatewayProxy attribute of the Recipient Update Service and the addresses that are currently on the object do not match the policy, the Recipient Update Service regenerates those primary addresses. The previous primary address becomes a secondary address"
Why not un-check the box "Automatically update...." on email address tab of the user properties. remove the smtp addresses stamped (that is if the user only wants the new ones and are least bothered with old ones) - once done, check the box once more - update RUS. That should stamp with new email address as per filter.
Since, you are changing the surname, this might not have affect on update - since the update option would undergo to check if the primary SMTP address matches as per filter, some times this is over looked.
What you could do, is to increase the diagnostic logging as per KB - 246127 and check why this user is NOT being selected by RUS in application logs.