Had a good long search and after finding hardly anything useful and nothing fully conclusive I decided a new thread was in order.

I need to know if there are Lua functions that forcibly open and/or close all exits. If there are not, is there a hacky way round it?

You can force the doors open by using the controller input that makes actors Fire. I haven't figured out how to close the doors yet.

Use an invisible actor to trigger it?

Controller.PRESS_FACEBUTTON is what you're looking for. When it's set to true, it either opens or closes the doors depending on their current state.

Thanks very much

Actually, Controller.PRIMARY_ACTION also works. There's a lot of redundant functions around.

Redundant but not identical. PRESS_FACEBUTTON is obviously a gamepad related hook, whereas PRIMARY_ACTION is a generic statement. There's situations where only one would be useful.