Add a Reset Preferences button or menu option
At present the user has to do that manually in a platform-specific way (cf. https://git.purrdata.net/aggraef/purr-data-intro/blob/master/Purr-Data-Intro.md#resetting-the-preferences), which might be more than users not proficient with the command line or Windows registry can handle. We already know what the necessary incantations are, so we might just as well go the extra mile and add a button for it.
Of course, that button should look RED and DANGEROUS and maybe launch a confirmation dialog, so that the user only runs this when she really knows what she's doing. :)