Sometimes updates are only necessary to correct a specific problem. You must replace a module of your applications under certain conditions, depending for instance on the existence of files or registry settings.
With LizaJet Installer you can easily do this, just define a new package that only includes the new module, and include in the upgrade script the conditions for downloading and installing.

 If you want to target the upgrade to  exactly one user, you can even check for the registration number of this end-user in the upgrade script.

Simply add a check execution condition, and create a script that checks for the license number. 

You can create a small package that only handles the check conditions, and only download the real package if the conditions are fullfilled. The overhead of your other end-users is minimal, only the end-users that really need the specific software will