Is there any way to create permanent settings (that won't revert to default after log-out) for the guest account and for the login screen in SL? I mainly just want to enable tap-to-click for both.
You can't retain guest settings. Just create a new normal user account, that's what they are there for.
If you want to have a guest account that has predefined settings; set up a normal account and then set it the way you like and copy there relevant settings and files to your specific language project in /System/Library/User\ Template/ and that will be loaded each time a guest logs in.