How hard is it to switch from P2P to Merge replication

Question 1: If we were to use P2P replication for a while how hard would it be for us to switch to Merge replication.

Question 2: If we were to do this (switch) would it be better to not use P2P replication for very long, or does the level of difficulty remain the same no matter how long we use P2P replication.

Question 3: Do people do this a lot, why or why not.

Thanks,