It seems the best way to do this is to add a `handler` callback to the modifier `PanelType`s.
It's actually a pretty elegant way to handle this customization in my opinion.
It also adds little shortcut strings in the menu (I had to add a new flag to the layout code for that).
{F8622018}
I'd like to get feedback on the shortcuts (whether there should be more, fewer, different, etc..), then do technical review after.