Comment by skulk

This all works in evil-mode as well, and by default you get the cool live-preview (not sure how to enable that for the vanilla C-M-%)

    :%s/\([0-9]+\))/\,(1- \#1))/

will turn

    1) one
    2) two
    3) three

into

    0) one
    1) two
    2) three