Mail changing and account merging is already available, although not from within the client itself.
Go to the stardock support website:
https://www.stardock.com/support/
To change email: "Need to update your email address or account info?" on the support page, then goto logon info.
To merge accounts: "Have products on multiple accounts and need to transfer registrations?" on the support page.
Note that accounts, when merged, cannot be unmerged. So I am not sure merging your account with your flatmate's is a good idea. But it can be done quite easily.
