You can redo the bottom, but you can't unravel it.
Put a long piece of contrasting yarn on a tapestry needle and thread it through a row of stitches above the seed stitch. With some cutting and picking, you'll be able to end up with live stitches on the yarn, from which you can knit the ribbing down.
The biggest challenge is keeping the yarn going through the same row, so you may have to readjust as you go, but it is doable.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry