Thank you, Mark!!
What utility can/should I use to re-edit each of my past photos with this profile? (I was using RGB)
And--this is an important question: will doing this "destructively" edit all of my .jpgs? If so, I won't do this for old photos.
Michael, In Photoshop you should be able to convert your previous images to your working space of choice. As far as I know this is not a destructive operation - but one thing to be mindful of. I would recommend NOT using ProPhoto RGB for 8-bit JPEGs. Use either sRGB or preferably Adobe RGB(98).