Can i use arduino + zigbee + bluetooth shield all together?
As long as the pins don't conflict.
This is why i'd like to dinamically change the 'master' zigbee's config from multipoint (setup to other zigbee end devices)
to point-to-point ('master' zigbee becomes a node temporarily)
I don't follow this. The master is a node, whether it is one of two or one of many. Are you saying that you want the node designated as master to take on a different role? If so, that could be quite a challenge. If you are using series 1 models, you can change MY and DL of the XBee attached to the Ardduino, to change from point to point to point to multi-point. If you are using series 2 models (mesh network), changing from coordinator (master) to end device (node) requires different firmware, which the Arduino can't manage.