Using systemctl edit via bash script?

I install Debian a lot. To do this I have a fully-automated preseed.cfg; at the end of the preseed, it downloads and runs a postinstall.sh script from my TFTP server, which does some additional customization. I'm in the process of switching from GNOME to LXQTE, and using SDDM instead of GDM. However, SDDM tries to start too quickly for my hardware. To get around this, I've been using systemctl edit sddm to add the following: [Service] ExecStartPre=/bin/sleep 5 This works great, and I'd like to automate this process by adding it to the postinstall.sh script. However, I can't figure out how to pass the file contents to systemctl edit via a bash script. How can I do this?