This is a very common configuration.
Your high-occurrence users of the software should be using User Subscription Licenses, and your lower-occurrence users of the software should be using your Team Subscription License.
The recommended way to set this up is to add your entire potential userbase into the portal, deploy the workstation software on every system, and then select the Team Subscription License Auto-Registration option. After that, you should identify and manually assign only the high-occurrence users to the User Subscription License (you can also invite those users by e-mailing them a link).
With this configuration, your high-occurrence users will be dedicated to the User Subscription Licenses. Any lower-occurrence user will be automatically registered to the Team Subscription License by simply starting the program.
There is no need to be concerned about having the same person registered to both the User Subscription License and the Team Subscription License. If this situation occurs, the software will always prefer the dedicated User Subscription License.
If you want to promote a user from the Team Subscription License to the User Subscription License, you can simply assign them to the User Subscription License, and that will be their preference thereafter.