Open up IS Boxer Toolkit.
Ensure the Characters tab is expanded (top pane).
Scroll down to, and expand Action Target Groups (still top pane).
Right click on, create a new ATG, call it whatever.
Left click on it (top pane), so it is displayed in the lower left pane.
Scroll back up to Characters (top pane).
Drag a character from the top pane, to the bottom left pane, which assigns it to that ATG.
This is the initial, on start up, state.



Expand Keymaps (top pane) and left click on one of them.
Right click on Mapped Keys (bottom left pane) and select New Mapped Key.
Call it whatever.
Expand the Steps, click on the 1.
In the bottom right pane, right click on the Actions.
Select >> New Target Group Action.
Choose the Target.
Choose the Action Target Group.
Choose Join or Leave.

You could easily go more then one Step.
So they can join/leave on press 1, and do the opposite on press 2.
You can also include Pop-Up Text, for the active window, to announce what step they're on.



When you have a mapped key, for example your DPS key.
You can set the target to a Toon, Slot, Character Set, Current Window, Other Windows without Current, or an Action Target Group.
Repeater Regions are the same, in that you can pick an ATG as the target, rather then a specific Slot.
That's pretty much it.



You know how to set your ATG state initially.
You know how to use mapped keys to add or remove toons from slots.
And can set the ATG as the target of a mapped key.