Hello ,
Please follow the below mentioned Kb article which explains the process of adding the Vsys license keys to the device:
# https://kb.juniper.net/InfoCenter/index?page=content&id=KB5518&actp=search
Afte uploading the device has to be rebooted for license to take effect.
It would not create any issues to your existing vsys. Please accept the solution or mark as Kudos if this resolves your issue.
Regards,
Rishi