The cross-project ID is based off the email used to signup/login. If you recently switched email addresses it may take time for the id to be resolved. I do not know of a way to manually merge them.
1st, to be clear, in BOINC there are two kinds of "CPID" -- there is a host (computer) CPID and a user CPID. are you referring to the computer CPID? ie, do you want, in effect, to merge the records for two computers? or do you mean something else?
