Simply a 4th Keybind, that adds a 3rd Power Active.

So in code it could be like

"key": "key.origins.tertiary_active"

:)

Probably not going to happen. If you want more keybinds, there is an add-on which provides additional active keys for Origins: https://www.curseforge.com/minecraft/mc-mods/origins-extra-keybinds