Saw in this answer that it wasn't possible in 4.7:
https://community.jaspersoft.com/questions/802872/how-can-i-force-particular-theme-url
Wondering if this has been updated.
We'd like to be able to create an alternate theme *once* and in the public folder, and allow users in orgs to access via URL param. Looks like the only way is to either set theme as global from root, or duplicate the theme in all of our tenants themes folders. Both are not ideal.