I rolled my Mavic firmware back to .700 last year, haven’t looked back since. Back then, I went the Dumldore route so it took a while, worth the effort though.
Some of you may know, I live just up the road from a football stadium so I’m permanently in the yellow, drives me bloody mad. Was also one of the main reasons for rolling the firmware back too.
Anyway, rolling the firmware back does allow me to take off in the yellow zones now, but it doesn’t stop the app itself from nagging me about it 
Funnily enough, just these last few weeks I’ve been getting heavily in to the modding of the GO4 app itself.
The reason for this is because I use the CrystalSky monitor I have no choice but to run whatever locked down version of GO4 that DJI choose to ship with each CS firmware update. There’s no way to roll the CS back, nor the GO4 app itself.
Soooooo 
I’ve been tinkering with the source code of the Andriod version of the GO4 app, with the help of tools like deejayeye-modder and the OG crew over on slack.
Today I was finally able to build my own GO4 app, with FCC enabled, version update checking removed, offline mode (no DJI login req), Google Sat Maps restored (the CS uses the shit ‘Here’ maps) and a few other tweaks.
Most importantly, I’ve been able to clone the app with a different package name and side load it on to the CrystalSky 
And it shows up properly in the Apps section of the CS too.
In all my testing I must have compiled 40+ versions before getting something I was happy with.
You’ll see in that screen shot some references to NLD. I also bought their Mod Client app which, getting back on topic, is absolutely brillliant!
But… not if you have a CrystalSky as you can’t replace the built in apps on the CS.
Anyway, yes, the NLD app is well worth the £20 quid mate, firmware roll backs are literally just a few clicks, as are parameter changes.
If you want to dig deeper, check out the open source utils, if not then NLD is exactly what you need 