I just did a
man synclient and the only file it refers to is
/etc/X11/xorg.conf. That's not definitive proof of anything, but it's a good place to start. If you're using Wayland instead of X, I have no idea.
I don't know exactly when that file gets read, but it's sure to be read when X11 starts, so if you replace it with a backup and restart X that should do it.
Doing so will get you and any other GUI users logged out in the process which is a bit inconvenient.
If you're going to be doing this a lot, then you could write a script that builds two commands/scripts (or just do it manually), one to modify the settings and one to put them back using
synclient. IIRC, changes made with
synclient take place immediately, so you should be able to undo anything you've changed on the fly.
If you run
synclient without any arguments, it will list all the current settings (before you modify things) so you can capture their values for the restore script. You'll have to parse and process the output yourself, but it's just key-value pairs, so it's not too hard.
I thought that maybe you could have a local user setup for X11, but it appears that this is not possible by design. However, the article shows a possible workaround for that if you really need it.