It would be lovely if Assign Background also assigned the other font’s intermediate layers (brace layers) in case they exist (with identical co-ordinates) in both glyphs/fonts. Thanks!
Btw, it would be even cooler if they were synthesized in case they don’t exist in the source font/glyph. That’s exactly what my Insert Glyph to Background script does. Very useful! 
Any ideas on this? I just started writing a post and then realised this is exactly what I requested a few years back.
Related, and even simpler task: Copy the foreground to the background for all layers in the file, i.e. “Selection to background” without selection, for all layers. Surely this must be possible without a script?
As someone who only very recently discovered the Assign Background functionality, I want to add my +1 to above request.
Select the glyphs in Font view and use Cmd+J, for all masters. Is that what you want?
The problem is that this does not cover the intermediate layers.
I’ll have a look.