[Help] how to modify system files with root access?

[bagbyte]

I've now tried in several ways to change /system/build.prop (phone rooted) but I had no luck.

Method 1: BuildProp Editor
I've tried using this app to change the file, the save succeeds, but after rebooting, the "original" file is restored and the changes are lost.

Method 2: Remounting the filesystem
I've tried remounting the filesytem:

$ adb shell mount
/dev/block/dm-4 on / type ext4 (ro,seclabel,relatime,block_validity,discard,delalloc,barrier,user_xattr,acl,i_version)
...

$ adb shell su -c mount -o rw,remount /
$ adb shell mount
/dev/block/dm-4 on / type ext4 (rw,seclabel,relatime,block_validity,discard,delalloc,barrier,user_xattr,acl,i_version)
...

After making my changes, if I try to remount with ro access, it fails. After rebooting the changes are lost again.

Method 3: Modify system.img
I've tried changing the file in the system.img, repacking the super.img file and flash it as single AP file, same result, the changes are lost. I've tried to decompress the super.img and remount it (just to check the changes were still there) and indeed they were.

What am I doing wrong?
Is there any way to achieve this?

 

[bagbyte]

I've found a good description of how the system and Magisk work:
- https://topjohnwu.github.io/Magisk/details.html
- https://topjohnwu.github.io/Magisk/guides.html

 

[ESTIMULO]

hello, i am trying to modify build.prop to disable knox and enable multiuser but changes are not persistent, have you found a solution with magisk?