After the license is set up, then anyone on the computer can use it - you can use a non-admin account to run Houdini normally.
You'll likely also need to use an administrator account again to refresh the Apprentice license when it expires, every 30 days or whatever.
If you prefer not to invoke Houdini itself from the administrator account, you should instead be able to just run the Houdini License Administrator, which is installed here:
/Applications/Houdini.../Administrative Tools/License Administrator.app