Vicleecy,
In my many years involvement with flight planning, and especially ReClearance/ReFile/ReDispatch, I have NEVER utilised an airport that is BEYOND the initial POA!
ReClearance/ReFile/ReDispatch airports, normally, are located along the route of flight PRIOR to POA! which leads me to the question "what is your routing EGLL-RCKH?"
Also, ReClearance/ReFile/ReDispatch is utilised to REDUCE FUEL UPLIFT @ ORIGIN or MAXIMISE PAYLOAD.
If you nominate a ReClearance/ReFile/ReDispatch airport that is FURTHER than your POA (Original destination) you negate the whole principle!
Cheers
thetexpat 