KPRIORITY
KeSetPriorityThread(
  IN  PKTHREAD Thread,
  IN  KPRIORITY Priority
  );

Routine Description:

    This function sets the priority of the specified thread to a new value.
    If the new thread priority is lower than the old thread priority, then
    resecheduling may take place if the thread is currently running on, or
    about to run on, a processor.

Arguments:

    Thread  - Supplies a pointer to a dispatcher object of type thread.

    Priority - Supplies the new priority of the subject thread.

Return Value:

    The previous priority of the specified thread.