Don't Sweat it. Your workflow is fine. There isn't any less "destructive" way to do it, and in fact I challenge you to spot any differences at all in image quality. ProRes HQ rendered just once should be identical to pristine ProRes HQ.
By way of comparison, you have to RE-render plain ol' ProRes 422 six generations deep before any image degradation appears... and who'd do THAT?
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA