24D How to change the list of values for Publisher for Self-Paced Learning item

I would like to add some publishers for the Self-Paced Learning items new to 24D. I have not found the list of values anywhere yet.

Since I figure this is likely under Manage Common Lookups, another question comes to mind. Are there some common lookup lists that cannot be added to? I'm trying to add a lookup in 24D and for some reason the Add is greyed out for me. I thought I used to have that access.