How to undo changes after saving the file?

[plumbergp]

I tested changing the color of skin in a photo. Saved it.

Reopened the file, could not undo the color change I did earlier via "undo paintbrush" in the edit.

AA
Possible to undo or revert to original part of an edited image AFTER saving and closing the file?

BB
How to revert to original unedited part of an image beside using layer mask via changing the background color?

Thanks.