mem_sleep_default ignored; adding initrd images permanently

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I'm using Fedora 28 Workstation Edition on an X1 Carbon which only offers SOi3. There is a guide (https://delta-xi.net/#056) that gives instructions on how to retrieve and patch the ACPI table to make it use S3. I've done the following:

• created a new CPIO Image named: /boot/acpi_override (according to the instructions above)
• added mem_sleep_default=deep to GRUB_CMDLINE_LINUX in /etc/default/grub and ran grub2-mkconfig -o /boot/grub2/grub.cfg
• when booting I pressed e to enter the grub configuration tool and added /acpi_override to the initrd line (before the kernel image)

However, /sys/power/mem_sleep still shows brackets around s2idle despite deep being an option. (which I obviously dont want to use). I can change that by using echo deep > /sys/power/mem_sleep as root which makes it persist as long as I dont reboot. The laptop will then enter the desired standby mode if I close the lid of chose suspend from the power menu. I also need to add the /acpi_override each time I boot which gets annoying easily.

So my two questions are:

• Why is mem_sleep_default=deep "ignored"? And what is the best way to set it manually?
• How can I permanently add the /acpi_override image?