How to configure /etc/systemd/system.conf before boot up

I connected my cnc machine to a windows computer for file sharing but i had some problems. Winodws file sharing only works if I write -- sudo mount.cifs //192.168.1.94/Router2 ~/WindowsShare/ -o user=ServerGenel,uid=$UIDW -- after every boot up. Unfortunately when the system is shutting down, linux wants to close the connection and it takes 90 seconds. I wanted to edit the default time to 1sec but I accidentaly edited the wrong one and system is not booting. I wanted to edit #DefaultTimeoutStopSec=90s but instead I edited #DefaultTimeoutStartSec=90s and changed the value to 1. Now when I try to boot, it fails. How can I configure this setting before boot up?

When I am booting I get a grub menu. When I proceed to boot, I get errors. I am sharing screenshots with you.   

I booted from a USB Stick and managed to find system.conf that I changed before. When I try to change it, it tells me that I don't have permission. How do i change it as administrator?

I tried it but unfortunately didn't work. The problem may be that I am not the user for that drive.

Problem Solved!

So, I ended up plugging the boot drive to a windows pc. In windows, in order to read and write linux partition files you need Linux File Systems for Windows by Paragon Software. After installing the software I edited the file. Unfortunately after editing boot drive didn't boot. I started recovery from a usb drive and reinstalled Grub loader and it worked!

Thanks for advice!