it is doubtful whether the plan is promulgated to en route class D providers
It is if you address it to them on AFPEx
I don't know the answer to this one, only to say that last time I was flying along talking to London Info, I was handed to Solent and the first question solent asked me was "how do you want to transit". I had addressed Southampton in the FP.
Try it and see and report back to us
