Reset individual Design customisation settings or the alternative

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I recently ran into a problem where I wanted to change the heading /title /h1 of one page on a website from 100px (developer specified in theme) to a smaller font size, as the title was so long it ran off the viewport in mobile.
To do this, I simply changed the size under "customization", but accidentally hit the "whole site" instead of "this page only" button. Ok - I was tired.
When I went back in to return to the larger size site-wide, I wasn't able to return to the original 100px, as the customization value only goes up to 60px.
I tried overriding this in "additional CSS" but it did not take.
I guess I will have to reset, (AARRGH) but before I do, is there any way to record or download the present settings? I will have to redo all of them, and there are quite a few. I did the site 2 years ago, and this would be a handy thing to keep with client records.

arlenesey