How to edit the user created date?
I haven't done this before, but if you have a module that loaded a user account, perhaps using user_load(), you can manually re-set the $account->created.  Clues given in the user_save() function.  Let me know how you get on...

code will look something like this:


$account = user_load($users_uid_here);
$account->created = $date_timestamp_here; // eg. REQUEST_TIME
user_save($account);