You aren't joining one ball of yarn to another. You're going back to pick up stitches that are being held until you can get to them. It's a completely different situation, but it's very easy!
Move the held stitches back on to your needle(s) and just start knitting, leaving a tail several inches long to be woven in later. It's that simple!
Give it a try and see how it goes! Good Luck!
As for unraveling, weaving the tail into your work will take care of that!