1. I believe that the answer to this question is yes, a slave with a pairing bit set will only try to pair with a master with a pairing bit set.
2. Yes, the pairing bit can be reset on the master device while the channel is open.
3. Yes, pairing information is only exchanged at the message rate. The Master puts its channel ID into every message it sends, so at 1 Hz, the master sends out it's ID once per second. Because it is included in every message, there is an opportunity to pair on every message, so message rate does not impact pairing.
FYI, there is also a device pairing application note in the DevZone, which is very helpful in learning about pairing:
http://www.thisisant.com/images/Resources/PDF/ant_an02 - device pairing.pdf