Bulk Resize existing images?

Hi, I'm trying to figure out a way to bulk-resize some old albums. Basically, I don't have a need to have them up in full-resolution (4 megapixel) anymore. I know that I could upload resized images, but I'd have to delete my old images, and then I'd lose all the comments and hotlinks to external sites.

I did a test to upload an image directly into my g2data directory, overwriting the larger image. This works, but the database still has the original full-size.

Without me killing my install, is it possible to edit the database and change the sizes to the new uploaded sizes?

Or.. is there some other better/safer way to do this? I'm trying to downsize my burningman images.

Thanks guys!
-chromatest
http://gallery.chromatest.net