I recently cut out my Cast On row and tried to unravel about 2 inches of ribbing. It was a pain. My stitches just wouldn't undo themselves (which I guess is the way it is when you're frogging bottom-up), so there was a lot of cutting and a lot of un-weaving stitch by stitch. Sticking in a needle in a destination row was a life saver (Amy has a great video on this). If you're just planning on un-doing the CO and not ripping further then it shouldn't be TOO difficult.
I'm not 100% sure if this is how your pattern goes or if you've already done this, but, I think you're supposed to fold in the bottom 6 rows of stockinette along the purl row, and then baste/sew it down on the inside. That type of hem always prevents curling for me.