So, I tried it, and it did in fact reset my rosters. Thankfully I had backups of my db and data0 files.
It took me a while but I found a way to make it work. When I edit the data0.big file to add the career.ini, it regens the .bh file which resets the rosters in the .db file. So what I did to work around it was edit the .big file, then replace the edited .bh file with my backup. Then I opened CM11 and regened the bhs from there with the edited data0.big file, which kept my rosters and had the modded career.ini
It took me a while but I found a way to make it work. When I edit the data0.big file to add the career.ini, it regens the .bh file which resets the rosters in the .db file. So what I did to work around it was edit the .big file, then replace the edited .bh file with my backup. Then I opened CM11 and regened the bhs from there with the edited data0.big file, which kept my rosters and had the modded career.ini