First off, just want to thank everyone who helped me with this little project. I'm very new to drones and I've only had my Phantom4Pro+ for just about three weeks. You guys have been great and I am learning a lot.
So I was able to get to 509 and it was really quite painless!
Initially, when I started Dumldore, and clicked on BACKUP, it threw a warning that the newer versions of firmware couldn't be backed up. OK, fine and I skipped attempting to backup the existing, latest firmware that went on last night. I decided to write the 509 bin I got from github and that worked perfectly. Hooked up the aircraft to DJI assistant2 to verify the AC firmware and then did a factory reset to nuke any settings that had been retained. Half way there!
After the aircraft update was complete, I set about installing HighTechPauper's RC
p4p+ firmware. I extracted the BIN file to a microsd, loaded it into the controller, went to settings, updates, and hit the three buttons to select "local update." Let it run through it's paces and then did a factory reset of the controller to solve the problem for the DJI GO app constantly crashing.
From there, it was all good! Still haven't flown yet due to poor weather but hope to get into the air tomorrow.