Controls system-wide behaviors (e.g., refresh rates, network settings); also requires permission to unlock.
Now for the fun part. Here are real, working tweaks that improve functionality without root.
SetEdit is a double-edged sword. It bypasses user interfaces to edit raw database strings. The app will let you input broken values.
adb devices
adb shell pm grant by4a.setedit22 android.permission.WRITE_SECURE_SETTINGS