That is not how Kodi’s keymapping works. A person wouldn’t change the system level keymap as userdata files stack and override.
The following guide should answer all your questions…
I’m guessing what you want it to add an xml file in ~/.kodi/userdata/keymaps/
with
<?xml version="1.0" encoding="UTF-8"?>
<keymap>
<FullscreenVideo>
<keyboard>
<rightbracket>ActivateWindow(1101)</rightbracket>
</keyboard>
</FullscreenVideo>
</keymap>
Except I’m pretty sure that isn’t going to work and I don’t think there is a way to directly keymap what you want without modifying the skin itself. What you can do without an issue is keymap directly to the locations that menu is pointing to. This is already done by default with menu opening the video settings, holding down menu bringing up the audio settings, and holding down stop bringing up the subtitle settings. You can of course switch around what buttons do what using that file Sam linked to as a guide.