Video playback in Photos

You can do it with a macro app like Keyboard Maestro .  

I just tested it out and it works as expected in the full screen playback.  It doesn't work in the Preview mode.  Keyboard Maestro has a demo version you can try out before purchasing.  

Also there are other macro apps available at the App Store.  Just search for "macro".

In my opinion it's the most powerful macro app available. If all you're going to use it for simple key remapping there are less expensive apps available.

I can change Safari's use of a css file and minimum font size with a simple key combination:

I used to use QuickKeys but when I couldn't remember the key combination it was entirely too difficult to find them. With KM it's a breeze.

Hi

We are not apple here, we are users like you - if you want to give feedback to apple, the only channel they might listen to is:

https://www.apple.com/feedback/photos.html