My honest opinion is that it isn't for the faint of heart! I crashed my P3Pro. Camera and gimbal were mostly intact. I disconnected the broken parts on the bottom (couple of plates, shock absorbers, etc. and a cable) and flew the thing just enough to verify that all was not lost. Then went to YouTube and found several videos about removing the body (the top is easy, the bottom - not so much!).
By far my biggest problem was the cable set. If you look carefully at the very bottom of the P3Pro (the advance may look almost identical - I don't have one so I'm not positive) there are two cables that plug in near the camera. I think one of them is a 4 or 5-pin cable, and the other is 7 or 8-pins. The crash had jerked the cable out of the end connector. I couldn't find any way to re-insert the wires back in the cable connector (it's moderately small molded assembly and apparently *not* designed to be re-used or repaired).
The destroyed cable is part of the "cable set" listed with most dealers in accessories and spare parts. Plugging in one end near the camera is obviously trivial. Getting the other end routed toward the bottom of the shell (I had to remove the USB connector and cable to make some room to manipulate things) was a tedious patience-demanding exercise. But it was far cheaper than a new or refurbed P3Pro - I didn't even investigate how much someone might charge to do what I needed.
Now, all that said, as bad as what I went through - the bottom part of the shell is worse! Virtually every other part *not* associated with the gimbal/camera, is on the bottom shell. Some of the cheaper drones I've worked on over the years had a reasonable amount of plug-in stuff, but my P3Pro isn't. There are no individual ESCs - "stuff" routes into a board. Motors are not plugged like they are in so many R/C aircraft - they're soldered.
My personal feeling is that it is indeed a challenge but, with a few moderately specialized tools, a magnifying glass and a lot of patience, it obviously can be done - there are YouTube videos to prove it!
One of the YouTube videos I looked at was created because that guy wanted to replace both the shells and wanted to paint the bottom shell. I'd love to paint my bottom shell also, but the whole process looked too daunting!
Art - N4PJ
Leesburg, FL