Started a webpage that now contains a lot of analytic data. Now that I have the client GA Tracking ID I would like to move the data I already have to that
It is not possible:
You cannot currently transfer profiles or account data from one account to another account.
Google Analytics does not provide any flexibility with importing, exporting, or modifying any past data. Any data you have in one account cannot be moved to another.
With GA, the only way to get data in to an account is directly via __utm.gif requests, usually through their JavaScript snippet, but that doesn't allow for any way to import past data, since the date is fixed according to when the data is sent in.
Further, the Google Analytics API is read-only, and doesn't provide any way to import or move data.
(This answer is slightly less true for Universal Analytics