What does a frog say? Rip-it, rip-it. :teehee: Frogging is just a less painful way to say that you're ripping some knitting out.
As for making your sleeve longer, yes, it can be done. The easiest way is to pick up stitches along the bottom edge and add ribbing or some kind of edge to it.
You can take out (frog) the end stitches, but you need to secure the knit stitches that are in place with a length of yarn first so you don't lose them. (See 'inserting a destination row' in the videos.)
I recently made some sleeves shorter this way, and though it was a pain getting the knitting out, the end result is one where you'd never know.