Don't know whether this will work, but you might play around with Workflow-ng and see if that gets you anywhere. The initial role granted upon purchase could give permission to access edition #1 - this initial role would be set to expire in 1 month. A Workflow-ng condition could be set up to grant a NEW role (with permission to access edition #2) upon expiration of the first role. Etc. This method can even be used to send automatic e-mails notifying the customer of the availability of the new edition.