Broken heel - cutting cast ?

Problem: broken heel with 3 permanent screws in it.
After 2 weeks I got a permanent cast yesterday Friday June 5th, 2009.
It hurts terribly, pills don’t even help
When I had a “soft” cast it was knee high, I cut it and made it ankle high
because it was killing me. It worked very well, cut the majority of pain

Question: If I do the same with this “permanent” cast, will that affect the time
and especially the quality of the … well, will it just recover right?
With lower cast will it be the same or is it dangerous from the medical
standpoint? Because with the tall cast it hurts very much and the wound (heel)
is constantly disturbed by the cast and I can’t put my leg down it is a pure
torture. When the cast was shorter everything was “great” as much as it can be
in this situation. At least it did not hurt all the time and I could put down
the leg and give it a rest
So, can I just cut part of the cast without making it worse for the heel to
heal?