Regenerate gallery thumbnails after changing thumbnail dimensions

I’m looking for a way to regenerate/re-create the thumbnails that WordPress gallery makes on upload, after you change the thumbnail dimensions in Settings >> Media.

I found this post https://www.ads-software.com/support/topic/189979?replies=4 but was thinking maybe there’s a better way now that 2.8 is out.

Any suggestions, ideas, comments?

Thanks!

(FYI, I do not want a CSS hack. While this works for some of the issues I have, it is not a solution to the full problem)