The easiest way would be to use an
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(just upload you save, change values you're interested in and download the modified save using a button at the bottom of the page). In my experience it tends to switch around the addresses of variables in games made with this engine so you might have to try a few times before you get the correct one (try searching for your current sanity value to limit possible options).
Important thing to keep in mind: keep your old save backed up, at least until you're done changing it and know the new one works. If you change the wrong variable don't try to fix it by uploading the modified save again but rather use the old one - changing the wrong thing can brick your save.