So if you cannot program it (also not via arduino using an API?) then it's
probably not possible to switch between point-to-point and multipoint communication...
or is it?
Point to point is a configuration setting (MY on one is DL on the other). Mulitpoint is also a configuguration setting, that has one XBee in broadcast mode (DL = 0). It is possible for the Arduino with XBee to dynamically reconfigure the XBee. It is not possible for the XBee to reconfigure itself.