This document proposes a COSMIC-based approach to analyze the impact of functional changes in UML activity diagrams. It classifies functional change impacts into three directions: internal impact, intra-level impact, and inter-level impact. It also identifies three categories of functional change based on their size: minor, moderate, and major. The approach is demonstrated on a sample activity diagram for a ticket vending machine. In conclusion, analyzing functional change impacts in UML diagrams using the COSMIC method can help decision making regarding change requests.