BuddyPress.org

You will need to make that child theme then. I would add to your child theme folder structure the _inc/css/ structure as you have edited the main style files simply copy them over to this child theme directory, your child theme style.css in theme root will call those files in the same way as default does. Copy over any main files you might have edited such as footer, header etc to child theme.

When you have all the files you have edited safely copied into the new child theme download a fresh copy of BP and replace the files you edited with copies of the originals that way you can drop back to the default theme if need be.