Read the statement by Michael Teeuw here.
Applied change to config.txt, MM fails to boot.
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 No, because if that kills it, I don’t know how to bring it back - what file to edit etc…? 
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 @richard238 It just modifies the config.txt for you in a save way. There is a bigger chance of you killing your pi doing it manually than using the config tool. 
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 Ok, when I get time, I’ll create a backup of the MM SD card first, and then try the GUI config tool. Thanks. 
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 Mine installation was successful. First I update rp3 
 #sudo apt-get update
 #sudo apt-get upgrade#cd MagicMirror/ 
 #git pull && npm install#cd 
 #sudo nano /boot/config.txt (add in config.txt and save)
 dtoverlay=vc4-kms-v3d
 display_rotate=1#sudo raspi-config 
 Advanced Options
 GL Driver
 G1 GL (Full KMS) OpenGL desktop driver with full KMS#sudo reboot ***I cannot remeber if I did this process or not 
 #sudo nano ~/.config/lxsession/LXDE-pi/autostart
 @xrandr --output HDMI-1 --rotate right (add to autostart)
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 Done through raspi-config, seems ok, boots and runs fine. sudo vcgencmd measure_tempshows 56.9C 

