I've done that with several lenses- copper tape on the back of my 50/1.1 Nokton and 35/1.2 Nokton. I use it with my M Monochrom, M9, M8. I've been doing that trick for over 10 years now- No Damage!
just spent all morning building a J-8 out of left over parts. Spent 5 hours building and testing. The thing was a mess, then the first optics module got stuck in place and the namering set screws were no match for the focus mount. The front ring is held in with two small set screws, and will often give way when unscrewing the optics from the focus mount. I ended up having to take it out the hard way, ie remove glass- and transferring the glass to a second module.
To improve the aperture motion for the J-8 and J-3: put a little Heavy Grease under the aperture cone. You have to take off the retaining ring, and then the screw that links the aperture ring/cone to the actual mechanism. I use vacuum pump grease. It's a pain in the butt.