Re-routing is quite common in the aviation industry, and there are 2 types, both of which are eligible for a compensation pay-out.
The first type of re-routing occurs when you reach your planned destination with a different flight number than the original one on your ticket. This is the most common type of re-routing and it often results in delays for passengers, which can vary from a few minutes to a number of hours.
The second type of re-routing happens when you reach your destination by travelling along a different route than originally planned. In order to be eligible for compensation for this type of re-routing, your delay must have exceeded 3 hours.