1: Always make a backup of files/folders before doing any changes ..
2: Goto your "Documents\My Games\Starfield\" folder
3: If you have a Data folder located here, Right-Click -> Copy or Cut and then Right-Click and Paste it to your game install folder (same place as Starfield.exe)
4: Goto your game install location - where you find your Starfield.exe: (ex. C:\Steam\steamapps\common\Starfield) or GamePass: C:\XBoxGames\Starfield\Content)
5: Download Modfix.cmd to your game install location placing it next to Starfield.exe (You can create/edit Modfix.cmd yourself if you like)
6: Right-Click Modfix.cmd and Run as Administrator 
7: Now you can install mods as you normally would with any previous Bethesda title (To the game istall location where you find your Starfield.exe)
8: You are done messing around with "Documents\My Games\Starfield\" location except for editing ini or custom run commands.
9: Seriously, you're done here go play. oh.. you can delete Modfix.cmd file now if you wish.

Q: Do I need to update when the Modfix version is updated?
A: No - Most of the changes are pathing that may have prevented some from installing the fix because of different ways the OS writes out path information (especially if you moved your profile to a different drive). If it worked for you already, You're good to go, no need to touch it again until you either reinstall your OS or if you delete the My Games\Starfield folder or if you delete the My Games\Starfield\Data Symlink)

Q: I get "You do not have sufficient privilege to perform this operation." when I run Modfix.cmd
     -or- Please run Modfix as admin and try again
A: Right-Click Modfix.cmd -> Run as Administator

Q: Will this overwrite my existing StarfieldCustom.ini
A: No, it will only create one with proper data if it does not exist already

Q: Will I lose my existing Documents\My Games\Starfield\Data folder?
A: No, If you followed instructions you would have moved this already however, Modfix will rename it to Data_TIMESTAMP where timestamp is the datetime of the fix applied - Follow instructions of Modfix once Modfix is complete. If you closed Modfix already, simply move the files/folders from inside the Data_Backup folder to your Game_Install_Folder\Data\ location. (Example: C:\Steam\steamapps\common\Starfield\Data\)

Q: I get "Starfield.exe not found. Please make sure you placed Modfix in the correct location and try again..." ?
A: See Docs, specifically Steps 4 and 5

Q: Can't you make Modfix move my files for me?
A: In short, Yes. I didn't because in the event you have mods there already, I will leave it 100% up to you if you overwrite existing files. This way, you cannot blame me for messing up your mods.

Q: I am getting "Access is denied. Cannot create a file when that file already exists."
A: Please rename the Data folder in Documents\My Games\Starfield to something else (ex. Data_Backup) (Thanks Veloxio!)
    The Modfix should have done that, buit if it failed you can manually rename it.

Q: I am getting "The system cannot find the path specified" like 4 times?
A: This has to do with directories not existing or being in a different location (Documents\Starfield) If you would, send me a Private Message and let me know (by pasting the path) where you would find your StarfieldPrefs.ini so I can try to fix it in an update.