You can create a license job, NSH based job to license servers.
Make use of the smart group you have for not-licensed servers in this job
And schedule or manually run this job.
A smart group should get automatically refreshed when the job is invoked, provide the user/role who runs this job has got access to these servers.
hope this helps.
Right button over a server --> Administration task --> Update Server properties.
The Update Properties Job Wizard opens. Just select "All Servers" as target and set a schedule that fits your requirements.