Once Glazed, Twice Fired?

Actually I have several somewhat related questions

1. I have some pieces that I used wax resist on for decoration. A couple of them I'm not pleased with after coming out of the glost fire. Can I glaze the unglazed parts and refire the pieces?

1. There was a question a week or so ago regarding reglazing and a couple of the replies mentioned that it would be best to reglaze with the same glaze. With that in mind.....There is a piece I want to try to reglaze that has a blue glaze covered by a clear glaze. Can I use the blue glaze to reglaze it or is this not a good piece to try to reglaze?

2. This question is kind of related to question 2....With a piece that already has two layers of glaze (both were brushed on the inside of a bowl and not put on too thick) would putting a third layer on be too thick? What can happen if glaze is too thick?

1. Again with the refiring.....Is there any way to cover up underglaze that has been fired with a clear glaze on top?

Thanks in advance. LMac