If you're having trouble because of FTL modifiers etc, here is an alternative method of implementing essentially the same thing with a Click Bar instead. Using a Click Bar is going to give you some added flexibility as well (with the exception that it only works when doing left/right clicks plus modifiers )

The key to making it work with a Click Bar is the underlying Mapped Keys. For my proof of concept that I just did to make sure this works before suggesting it, I made one Mapped Key that's going to send mouse3 (middle button) when I left click. I arbitrarily called it "press mouse3". It has no hotkey, 1 Step, and no special options. Step 1 has 2 actions. The first action is a Sync Cursor Action with target being "Group (others in):healers" (whatever you were using as the target for your Repeater regions). The second action is a Keystroke Action sending Mouse3 to "Group (all of):healers". The targets I picked mean that the cursor will always sync on any healer I'm not playing at the time, and Mouse3 will go to all healers even if I'm playing one.

Then my Click Bar for this test has a single button on it, with one action on it (press mouse3) for Left Click and target=self (this target is effectively who hits the hotkey for the mapped key, and since the mapped key has the real targets built in, we want the current window to hit the hotkey, not all windows and not all healers). To get the same appearance as shown in this thread, I set the Color for the button (click on the box next to Color, to the right of Name) to 00000000. By default it's FF000000 with the Alpha channel set to 255, which is opaque black. This changes it to completely transparent. And it's going to have a white border by default.

I set the Cell size to be large enough to cover the desired portion of the healing addon. This is less convenient than resizing a repeater region, but a little bit of trial and error gets it done right.

Assign the Click Bar to the character set, position it in game, and voila. Repeaterless healing with the same capabilities as described in this thread without having potential problems from alt,ctrl, or shift being permanently held down while in the region.

Enjoy

p.s. Owltoid, this should get you what you're looking for