There are a number of ways you can do this, based on your business requirements. If you have a specific date for the start of phase 2, you could circumstance key rules based off that, so that you don't go down the v2 path for v1 items. You could also use a property to indicate which version a given item is in and then use when rules to direct the item down various paths. Much of it depends on exactly how differnt phase 1 and phase 2 are and if there are single points where things diverge. You could also get really drastic and make p2 flows that are entirely different, so existing p1 items will stay in the p1 flows and you can modify rules in both versions, as you see fit without any sort of overlap.