Well, with any software you could use a modifier key quite easily.

Macro on "1".
#show Spell
<Insert Assist Here>
/cast [mod:ctrl, Target=Focus] Spell; Spell

This will cast at your focus, when the Control modifier is held, but cast at whatever your normal target is otherwise... as determined by the assist conditions in the macro.




I'd recommend IS Boxer for a true toggle type effect.

You can build a mapped key, which executes on press and release.
Set the mouse button as the hotkey for this mapped key.
Give it two steps.
The first step loads/enables an alternate Keymap (set of mapped keys).
The second step unloads/disables the alternate Keymap.
If you wanted to use the same keybinds as your normal mapped keys, the first step could also disable the normal keymap, while the second could enable it again.

In play, you'd have something like...
- Pressing "1" has all of your slaves auto-assist (via FTL, which is done by IS Boxer) the active toon, and then cast whatever is on the "1" keybind for each.
- If however, you were to hold the toggle (mouse button), then the normal FTL DPS Keymap is unloaded and the alternate Keymap is loaded in its place. So pressing "1" does whatever is in the alternate mapped key, instead of the normal default action. And when you release the mouse button, the toggle effect ends and everything is normal again.