There shouldn’t be any problem if you update your Generatepress Theme, always if you did not modified any core file.
If your modifications were only at the level of the customizer settings then you can update without problems.
But if you’re a wise person, you know you need to have your backup at hand in case everything goes wrong.
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Regarding the Child theme, if you create a blank one following this instructions https://generatepress.com/forums/topic/how-do-you-make-a-child-theme/ you shouldn’t lose any customizer settings (that has been my experience) but you’ll probably need to reassign the menus and widgets