Question about DLC/custom skins


I was wondering if the skins in the skin mega-thread on the top of this forum **replaces **the original SF4 costumes, or **adds **them (ie, adding additional costume slots)? If they only replace that means whenver I want to use the original SF4 costumes I gotta paste back the original files right?
I was also wondering if I purchase the official DLC costumes for SF4, when Super SF4 comes out for PC, do I have to re-purchase those DLC’s again or do they somehow transfer over? And anyone know of an exact date of when Super SF4 will come out for PC?