I would like to assign a permission set licence to an existing or cloned permission set. Unfortunately I am only able to assign a permission set license when creating a new permission set. Does anyone know if this is possible?
Cloning copies the existing license. This ensures that the cloned Permission Set has all of the same options available as the original. If you want to clone and change the license type, pull the file down in an IDE, copy-paste to a new file, make any modifications, then deploy the new file. If any permissions are specified that are invalid for the new license type, the deployment will fail, and you'll need to modify the XML file manually. The license type is fixed for a permission set once is created, and cannot be modified afterwards. Again, this restriction ensures that you can't change the license type in a way that would allow invalid permissions to be in the Permission Set.