Greetings was698002 and welcome to the forum.

All but one of the files in /etc/X11/Xsession.d are owned by root and read-only.
However, one file, 45knoppix, is owned by root and also executable.

I add a synclient command to this file, at its end, to tweak my touchpad.
This is slightly simpler than adding a new file just for this one tweak.

Quote marks are not necessary for the command.

Of course, you'll need to have persistence working for this to make a permanent
change to your system.