Hey guys here are my observation so far.
Warranty
I am not an expert in this area but Im sure apple can deny your warranty claim if the iMac is not put back together correctly. That said, I recently had the screen replaced on my 2011 27 imac, which had a diy CPU and SSD upgrade. My guess is that they did not care since the LCD problem had nothing to do with my upgrades but YMMV.
SSD install
You can replace the factory HD with an SSD without the fan running at the max RPM but AHT will report a hardware error related to the HD sensor. I dont like the idea of a fusion drive since I love using symbolic links but Im currently testing the machine with a diy fusion install consisting of the a Samsung 830 SSD(internal) and the original 1tb HD in an external usb 3.0 enclosure. I having been monitoring the system with IOSTAT and everything seems to be running perfectly. Personally, I would not risk running fusion with an external drive.
CPU Upgrade (This will defiantly void the warranty on the logic board)
I decided to buy this machine from my friend and I am going to attempt to install an intel i7 3770s very soon. If the cpu upgrade works I will cancel my order for a maxed out 27. This was my first experience using a 21.5 imac, I thought I was going to be disappointed with the lower resolution but I was very pleased. I guess after 8+ years of using apple 30 and 27" displays my eyes need a break.
Adhesive tape
-Do not use 3m 465 tape, it leaves a messy residue thats easy to clean up but you might end up scratching the paint on the back of the glass while cleaning it up.
-VHB tape peels off like the original tape but Im concerned that the bond might be too strong if used to seal up the entire bezel. I am currently holding the lcd in place with four 3 strips of 3m 4926 tape.
I dont plan to seal the iMac up completely unless i have to take it to the apple store for repair. I am very satisfied with using small strips of the 3m 4926 to hold the display in place, it still looks brand new with no gaps and the lcd will not come off the frame without some deliberate effort. Eventually OWC or iFixit will post the correct tape to use.
FOR THE CRITICS
Your opinion means nothing to me. Its my money and I will destroy any apple product that comes my way.