Process aware Information Systems (PaIS) have an ever-increasing importance in Enterprise Information Systems for supporting both their intra and inter-organizational processes. However PaIS still have important issues to address, including flexibility of inter-organizational (i.e., collaborative) processes before their definitive acceptance and their use in companies. This paper addresses this issue advocating (i) the modelling of collaborative processes as BPMN collaboration, (ii) the use of the version notion to deal with collaborative process flexibility and to make process instance migration easier, and (iii) the introduction of 6 new adaptation patterns which are high-level operations for collaborative process schema update.