You can republish old content with new dates without breaking the URL. Today I revised a post I'd written in 2008, but I set the publication date to today's date.
The post republished with today's date and is ordered correctly on my tech blog page, but it kept the old URL embedded date: tech.kateva.org/2008/09/os-x-major-version-updates-my-approach.html.
It's probably always been that way, I just never tried republishing before.
It's something I'll do more often now.