Does anyone have a strategy of attempting to reroute in the last moment if it becomes evident that you are not going to clear, paying a changing fee but getting on another flight with a confirmed upgrade? How close to the flight can or should you do that? Does anyone have a system they want to share? What would be the pros and cons of this idea?

For example, switching from ORD-DFW-HKG to ORD-PEK-HKG, if there is C space open on ORD-PEK.