I don't know. Generally you have to sacrifice the handle to save the knot, or sacrifice the knot to save the handle. I have never steamed a knot but I have seen handles and in some cases, the hair, damaged in steaming. Are you willing to risk losing the brush to maybe achieve your goal?
i wouldn't try that; i think you will ruin either the knot or the handle. i think you would be money ahead to just sell the brush and get a new one that has the dimensions you are after.
I thought of so if that but I really don't want to risk damaging it. It'll probably be up on the BST soon because I am quite picky despite it being a great brush.