Maybe I don't understand properly what you mean, but isn't this already in the game?
If you look at your powers tray and hit the little button on top to the far right, it should list all powers you have. They should be listed, and you just drag and drop.
The powers currently activate then stop after about six seconds. By toggle I mean press 'reroute power to forward shields' and it remains 'on' for that one shield facing, until you turn it off by pressing the keybind again.
Try key binding ++left and ++right and using those, it toggles left and right turns without having to hold the keys to keep turning, you might see what I'm trying to do with the reroute power to shields. The ++ does not currently seem to work with the / commands for reroute power to shields.
I can see this being useful. As it is most people do multiple action key binds to make sure they're constantly spamming rebalance shields, so a toggle to one facing could be good, would cut on the keybind spamming.