[Reason077]

Instead of attaching the motor bracket with a binder clip, consider sticking it down with some sort of removable adhesive?

3M command strips should be very strong/secure, while also allowing for adjustment and will detach without residue when the time comes.

[singron]

I think you could use the two shafts to align and attach the mounting bracket by drilling two holes the proper distance apart. Drilling holes is pretty easy compared to cutting straight lines and I think most people are more likely to have a drill. If you use a piece of wood, the additional thickness can help the shafts to keep the wood perpendicular. You might not need any additional fastener, and the lack of fastener could help it return to a neutral position after operation rather than migrate. Also, slowing down the stepper motor can reduce unnecessary forces and the likelihood of malfunction.

[tjoff]

I'd never trust that it will hold and detach without residue, but that is probably my ignorance talking...

I own a 3d printer which makes most of these projects look like the perfect fit for a 3d print (even when there are far simpler solutions). So that is what I'd do :)

[itslennysfault]

I'd cut a block of wood to fit snuggly to the left of the knob, wedge it in place and screw the stepper in to that.

.....or just screw into the AC unit somewhere discrete and hope no one notices.

[throwway120385]

Just putty over it and get a slightly matching high-gloss or semi-gloss enamel and nobody will notice it. I've put tons of holes in things in rentals over the years and basically nobody will care as long as you restore it to like condition when you leave.

[prmoustache]

Have you ever seen a landlord check that kind of things really?

Unless you have made a mess with wires getting out looking like a fire hazard in waiting I don't know anyone who would stop at 2 tiny screw holes. Heck the landowner may not even remember the unit was not made that way in the first place.