I've never replaced a 3DS screen before but I have successfully replaced several iPhone and iPod screens so I imagine its almosr on the same difficulty level. So here's some advice; be very very patient while disassembling and reassembling it, watch a few YouTube videos ahead of time so you can find one that you feel comfortable watching while you disassemble your 3DS, and try not to get too frustrated if you do something wrong and just calmly fix said mistake.
Good luck man.
