You can assign any name you wish to each of your libraries in the list by first selecting the library, and then clicking on its name to begin editing it (just like renaming a file in the Finder). Alternately, you can control-click on the library and select “Rename Library” from the contextual menu that pops up.
When you first add a library to PowerPhotos, it will be given the same name as the library package has in the Finder. The Finder name and the name in PowerPhotos are separate though, so you can change one without having to change the other. For example, if you’ve added a library that belongs to another user, and that library is named simply “Photos Library”, you can give it a different name in PowerPhotos such as “Bob’s Library” without affecting the name of the actual library on disk.
When renaming a library in PowerPhotos, only the name in the PowerPhotos library list will be changed, and the library will keep its same name on disk. You can also change the name of the library on disk separately via the Finder. When you bring PowerPhotos to the front, it should see the change and update the path for the library to point at the new location. PowerPhotos will not automatically change its own display name for the library in this case.
If a library shows up in red in the list, it means that the package for that library does not exist on the disk (e.g. it was moved or deleted), or the disk the library resides on is not currently available. If the library is kept on another disk, insert or connect the disk, and the library name should change back to black, indicating the library is now available. If it’s a library that you intentionally deleted or no longer need to access, you can use the “Remove Library” command to remove the library from the list.
Renaming issues on macOS Monterey and later
When renaming a library in the Finder (not in PowerPhotos) on macOS Monterey or later, it can sometimes cause an issue that will cause PowerPhotos to either hang when trying to read the library in its new location, or sometimes display the library as being empty. If you experience either of these behaviors, especially after renaming or moving a library, logging out of your account and logging back in is often what needs to be done to get things working smoothly again.