Gluster users - Feb 2015 - How to convert from 2 node replicated to 4 node distributed-replicated

Hi,

Is it possible to convert a 2 nodes replicated volume to a 4 nodes
distributed-replicated volume? If yes, is it as simple as just issuing the
add-brick with the two additional nodes and then start a rebalance?

And can this be repeated ad infinitum? Let's say I want to add again another
2 additional replicated nodes to a distributed set?

Regards
ML