Wait what? I'm not sure if I understand what you're gonna do.
- So you knitted and completed a stockinette scarf.
- You want to take it apart piece by piece.
- You're reknitting it into a ribbed work.
If you're doing that, isn't that the same thing as completely unraveling your finished stockinette scarf completely and starting all over again?
If I were you, I'd drop the top stitch you wanna make a purl/knit column, frog the entire column, and use a crochet hook to remake it into a different stitch. I did that once after realizing that I didn't like the stockinette stitch on a scarf I made. There's a video somewhere on this site about fixing mistakes without unraveling the work. :D
If I interpreted your post completely wrong, then disregard everything I just said :P