since Photos is never modifying the original image file it imports, it would be best to rename any image file or video file in the Finder before you import it to Photos, if you want to have more descriptive filenames.
I prefer to add descriptive titles to the photos, for example by typing a title into the title field of the Info panel. The titles can be displayed below the thumbnails in Photos, while the filenames are not shown in the browser.
The titles can be used as the filename, when exporting an image file from Photos.
There are few user supplied scripts to help with batch changing the titles:
- Script: Batch Changing the Title to the Capture Date
- : Batch Change Title to Capture Date-Description-Padded Sequential Number
- : Script: Batch Changing the Titles to the Filename w/Extension
See the User Tips for more: Thematic Index to Photos for Mac Related User Tips: