Separate Opacity per Paintmode? or eraser toggle other than "e"?

I recently switched to a tablet with no eraser on the pen. I’ve enjoyed using the “e” key at full opacity with this setup, to switch to the “erase” paintmode of the current brush. The problem is, I often need a softer opacity to draw, and a hard opacity to erase. This isn’t a feature request, because I don’t know if there is an obvious alternate solution.

I added the eraser to the “5” key as a shortcut, but then I also have to add a pencil shortcut, and that takes my hand away from the home keys. Is there a key that toggles the eraser, with it’s own opacity and setting, just as if i had flipped my old pen?