[One (M7) Q&A, Help & Troubleshooting] Bill720:
Fixed!... but with strings attached

Just to provide some closure for this fiasco, I did finally get the HTC One fixed and reassembled properly. Here's a quick recap:

Following the initial successful screen replacement, I bought a replacement camera module and back cover for the phone (because the problem persisted with the back cover off and because I had ruined the original back cover during the original disassembly). Upon installing both, I promptly reassembled the phone and discovered that the SIM card slot was no good on the replacement screen assembly. Talk about a major bummer!

From here, I was actually able to carefully remove the (shiny new!) back panel without causing any damage and requested a replacement screen assembly. Replacement was the wrong color. Two weeks later, the correct one finally came in, and I went through the (rather convoluted) procedure of painstakingly taking everything off of the screen assembly and placing it onto the replacement... again.

This time, everything worked, (including the SIM slot) so I slapped the back cover on, but was disappointed to find that the volume-down key had come out of alignment during the second back cover install. Also, the vibration motor had worked its way out of place and was rather noisy. For a third time, I ventured back in and managed to get the back cover off without causing much additional damage (there are some small marks on it now, but it still looks a heck of a lot better than it did before) and stuck some adhesive to the side of the motor in order to hold it into the slot better. I also performed the final snapping on of the back cover more carefully.

Finally, the phone is reassembled and fully functional. Camera photos no longer have a blurry edge, but are occasionally blurry either all over or in certain places. It is capable of taking completely clear shots though, which is interesting. Regardless, I've pretty much given up on getting this thing to perfection, and because of the fact that it isn't my daily driver, the camera not working right is not a dealbreaker. At any rate, it seems like finding a properly functioning camera module for this model is nearly impossible. Also, the right (bottom) speaker's volume is now sometimes a little quieter than the left (top) one, depending on the volume. As before, the MicroUSB connection still doesn't allow the cable to plug in all the way, which makes it really easy to accidentally disconnect, but it does still work fine.

With all that said, I've attached a picture of the repaired phone along with a new old-stock Incipio Feather grip casing that I found locally. The Incipio fits pretty nicely and I really like the feel of it, but debris sticks to it amazingly well. Even something as simple as wiping it with a cloth will leave behind a whole covfefe of specs. Liquid baptism and air drying is the only way to fully clean it.

TL;DR? Don't break your HTC One in a way that requires disassembly or repair. Ever. Even if the camera sucks, be thankful that it is fully functional (if it is). If you do attempt a repair operation of any kind, test the SIM card slot and camera (and speakers) fully before putting the thing back together and mind the volume keys as you put the back cover on.