If you push the pistons all the way back in, you have to pump the lever a few times to get it to connect and then surely the pad spacing is reset to whatever rotor width you now have?
Mmm, it sounds like a nice theory but I’ve found that sometimes the only way to increase the spacing is to open a bleed pooter and let a little fluid out.
Nor as pads wear.
I think you can bleed a brake up for Xmm of rotor width though and if you then fit a thicker rotor it'll be rub city right?