'tis the Commanders choice, whether he wants to comply...or not.
In itself that statement is true. Commanders have the
choice to ignore (or not) ATC instructions at any time. Whether this is a wise thing to do when those instructions are for the maintenance of separation is quite another matter. If ATC say "Turn right heading 300 degrees, descend 3,000 feet" and the Commander decides that he'd rather go left and climb to 5,000' and that brings him into direct conflict with another aircraft, then he'd better start getting ready for the inquiry. And obtain his own tea and biscuits.
I think
PhoenixRising has said it all in a concise manner a few posts ago.