Whenever a new FL release comes out, I back up my current working setup. I do it by taking the entire DSD+ folder and copying it to a new (backup) folder. That way, if anything bad happens, I have a recovery route. Then I copy the new FL files to my existing DSD+ folder. That way, any DSD+ shortcuts I have on the desktop keep working, and the Windows firewall doesn't need to be updated to get TCP linking working.
Hm, if you're upgrading from 1.101 to FL, you'll be switching from FMP to FMP24. Not sure what problems (if any) you'll run into. Shouldn't need to edit anything in FMP24.cfg, I wouldn't think.
I'd say back up your current DSD+ folder by copying it, or make a new folder for FL and copy all of your old DSD+ files to it. Then copy all of the FL files to the folder you'll be running FL from. That means overwriting some old 1.101 files (DSDPlus.exe, some bat files, and so on). Then try monitoring your NXDN system and go from there. FL will follow the control channel if it rotates, don't remember if 1.101 does that.