Miłosz Bolechowski wrote in to tell me that using Automator to change the date was silly because all of it can be done in Keyboard Maestro. This is a really complex version, but does work much faster than using Automator (my method).
I actually had no clue just how easy it was to grab files from Finder in Keyboard Maestro, so this is incredibly helpful to me long term as well.
Thank you to Miłosz Bolechowski. This is awesome.
(You’ll probably need to translate the page, but the last link in the post is a zip to download the macro.)