My 3DS also had a colored frame attached to the touchscreen that was attached with adhesive. This came off reasonably well by prying with the spudger, though I damaged the old touchscreen. The adhesive seemed to be gone after this, but did not give me issues after reassembly.
Reinserting this ribbon cable is quite difficult. I found opening the case so that it sits upright at a 90 degree angle helps. The first two times I tried reassembling the top display did not work. Turned out that I was not inserting the ribbon cable in enough. I used tweezers to push this in by gently grabbing the ribbon cable. I was continually inspecting the cable for damage but apparently did not damage it. If anyone has a better idea on how to reinsert this cable I think others would greatly appreciate it.
I second the one who suggested the Whia 273 PH000x40 screwdriver. I had a terrible time unscrewing these screws, and almost stripped them using a cheaper #000 screwdriver. Also tried a 3/16" flathead and destroyed the screwdriver. I bought the Whia and glad I did. It fit perfectly and did not slip at all. DEFINITELY recommend purchasing this high-quality screwdriver. Cost about $10 but well worth it to avoid the hassle.
My iPhone is about 2 1/2 years old and battery life is getting a lot poorer, drains fast on standby and shuts off at 20%. Followed the instructions and like most it went well but had no carrier signal the first time. Took advice on bending the grounding pin up more, and that fixed the issue. I suggest that the instructions be revised stressing the importance of this ground pin, and noting that not having it positioned correctly results in the no signal issue.