How to make minor customization to emacs theme colors

Question

I'm a fan of gruvbox, but would like to slightly change the white colors to make them less intense. Is there any easy way of changing this line:

(gruvbox-light0 "#fdf4c1" "#ffffaf")
to this:
(gruvbox-light0 "#ffd7a6" "#ffffaf")

without creating a completely new theme file?

I'm aware of this sort of solution:

(custom-theme-set-faces
 'gruvbox
 '(font-lock-comment-face ((t (:foreground "#DFAF8F"))))
 '(font-lock-comment-delimiter-face ((t (:foreground "#DFAF8F")))))

but I'd like to change the color in one place, so that everything set to gruvbox-light0 is updated.