I don't know how it all works for sure but the social worker should be able to guide you through it.
From my understanding of a having a directed donor & going to a paired donation is this. You want to donate to Mary, you are not a match with her but are eligable (healthy) to donate. Joe is eligable to donate but doesn't match his buddy Steve. Mary is still your "person" but your kidney actually goes to Steve & Joe's goes to Mary. As long as you follow through with your donation, Mary is guaranteed a kidney. If you opt out, you & Mary are both out of the pairing (even if Joe matches her perfectly)
At any point during the process you (donor) can back out. The reason will not be given to the recipient. I don't see why you couldn't decide to go the route of a directed donor &/or a paired donation.

@beckyjohnson I was approved to donate directly to my husband but we were still open to a paired donation situation to find a better size match for my husband - that's exactly what they were able to do. My husband received a kidney from someone in Florida and my kidney went to someone in Arizona. It did not matter to me where my kidney went, as long as my husband was able to get one - although it really does make me happy to know that in this process we were able to help another person in need! I am hopeful that the person that received my kidney is feeling as well as my husband is now! His progress has been amazing!