There's a ton of debate whether Ford can or cannot deny a warranty claim simply because it's tuned. I'm not going there ... you can search and read those for yourself.
If you are still afraid about voiding your warranty, do what most of the other guys (and I) do ... return it back to stock a couple of weeks before you take it in for service ... and re-install your tune after service. This will also avoid the problem should your dealership install a new program on your PCM while it's in for service.
As for installing, just follow the instructions carefully ... it takes 10-15 minutes to do it. Just don't freak when you hear the loud pop come from your stereo at some point. It's normal.
After you do it a couple of times, you learn at what point you can go back into the house for a while .... and return to fine your truck ready to go.