Unable to edit build.prop etc

[lukesan]

Hi Gents, Just received my Poco F1. I also have a redmi note 5 AI. I just unlocked the bootloader of the F1 yesterday and installed TWRP, the latest Pie rom from the site here and magisk v17.1
Now I wanted to edit the build.prop and swap the video microphones, yes Xiaomi screwed up left and right again, in the mixer_paths_tavil.xml file.
I used root explorer which seems to have root rights ... but I cannot change the files at all it seems. I also tried with Magisk v17.3 but exactly the same.
What am I doing wrong?

 

[Wizard84]

Try this : boot to TWRP go to mount, check system then reboot to system, now you can modify files with any root explorer.