Setting defaults for Magic Mouse
This is a two step process. The system make all new accounts from this template:

/System/Library/User Template


Unless you need to only change a specific localization, you'll be putting files into /System/Library/User Template/Non_localized/Library/Preferences

The two step process is knowing where to change a file and what change to make.

I don't have an answer to the second part (no Magic Mouse handy), but you might be able to do that part yourself. If you make a new account and change only that mouse preference and dig through the ~/Library/Preferences to isolate the file(s) that encode that change (sort them by date and the newest files should be the ones you changed to configure the mouse). Second, you need to copy that file into the default user template so that when the system makes a new account (guest account or any new account), that user gets the modified mouse settings you have copied into the template to replace the default values for that setting.

An alternate method is to look inside the file(s) to see if the settings can be written easily by a sudo defaults command:


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