I did it. After reading posts like this: Tired off .500 so I am back on .400 I finally took the plunge and did this for both myself, for the Mavic community, and because frankly I don't like the idea of being forced firmware updates that then cannot go back. I'm not going to go into a philosophical spiel here, so suffice it to say, the window of opportunity to do this was quickly closing, and it was now or likely never.Most of the credit goes to Robbyg for his detailed explanation of how to do it, and BorisTheSpiders whom Robbyg also had given credit for, for coming up with the VM idea and doing some of the initial testing.Unfortunately, I'm still in FW 200 and have no plans to upgrade to 400 anytime soon. Plus, what I'd really like to find out is if with this VM someone who is 600 and/or above could successfully downgrade to 400. I believe so yes, but it is not tested of course so I'm not sure.I used VMWare Workstation 12.5.5 and the VM guest OS has VMWare Tools installed. By default the virtual Network Interface Card is turned off in all three snapshots. The first snapshot is that of the OS configured, and with DJI Assistant installed and ready to go and make backups/snapshots, the second snapshot is the Mavic's RC snapshot for flashing firmware 400 and the third snapshot is the Mavic aircraft itself's snapshot or flashing to firmware 400. Again, the virtual NIC is turned off, there is no reason it would even need to be turned on. I did have to add virtual USB controller, and so make sure in Services.msc that you hadn't disabled or otherwise turned off the VMware USB Arbitration Service.The VM is in a folder just called VM. The name of the VM is "Windows" and the actual VM file is called Other 64-bit.vmx , so from the main VMware Workstation interface, just go to "Open A Virtual Machine" , browse and navigate to the Other 64-bit.vmx file, open it. then in the menu of Workstation, go to "VM", then "Snapshot" and select the appropriate snapshot depending if you wish to flash the RC or the Mavic itself back to 400I compressed the whole VM and associated snapshots and files and whatnot using 7zip and also but an encryption password on it. Everything altogether, it is called MAVIC-400FW.7z and it is about 5.16 GB in size. It unzips to about 15 gigs total. And inside contains an .apk of DJI Go 4 version 400, and of course instructions, and also as well the VM itself in said folder called "VM". (inside of which contains the Other 64-bit.vmx file) It also contains some PAR files for error checking, redundancy, and to prevent bit rot if you plan to store it or years. I created that using MultiPar.I'm uploading as we speak. May take me a few hours though. For those of you who are higher than version 400 and would like to test going back to version 400 (especially assuming once DJI makes this impossible to go back that far by removing 400 as an option, which likely they will do once the Goggles come out etc) I am willing to give you the link and/or send you the entire file on a microSD card if you really don't have the bandwidth to download, so PM or get in contact if interested to test this out to see if it really works.For those without paid version of VMWare Workstation 12.5.5 for the Linux and Windows versions you can download the fully functional 30 day trial without obligation.< MAVIC-400FW.7z >MD5: 4B1C15F2CDED8D9EA12EC74201C24454SHA-1: A9B95275CC33688EE66EC443ED27A6F2D9FE2600SHA-256: 08ADFE081AEB40D57DA4E2B0B85FCF6CECA4A064EC07B0498BE79CE270F09B32SHA-512: 3CCCE1BADC124F1CD71394F1287767A7BEEC594CB023575D578F8AECB2E055C47E41E8B30BFCEF2C2B198630AB881F8B3AE70985500D00C8D51D94FEEE043615