In Settings app: system setting: Developer mode enable Developer mode and allow Remote connection. Write a password (try to invent long but easy to write one) and save it. (Don't touch Allow developer updates!)

Start Terminal app. Because you want to edit system files, run command devel-su and give it the password you earlier gave for Settings app.

Enable mer-tools by giving commands:

ssu ar mer-tools
pkcon refresh

If you already know how to use vi editor, you can skip this step. Install easier to use editor by giving command:

pkcon install nano

After that go to directory to edit files, take original version aside in case you want to restore the original and edit the file:

cd /etc/mce
cp -ip 10mce.ini 10mce.ini.ORIG
nano 10mce.ini

CTRL+X to exit from the nano editor. Commands are listed at the last two rows when editing file.

WARNING! When editing system files it might be possible to brick your Jolla.