Previews is basically just a more visual Alt+Tab together with some much needed extra capabilities to make switching between apps and windows more intuitive.
The visuals update - just not on a frequent basis for videos!
Previews uses a global keybinding method we designed. To remap stuff:
Create a folder called ~/.local/share/budgie-extras-daemon
copy the appropriate .bde found in /usr/share/budgie-extras-daemon into your local folder that you created above.
Edit the command you want in the .bde files that you want to bind the shortcuts with.
Logout and login.
As to “Above tab” - no idea - “`” is above my tab key!