Well for me, the underlying principle here hinges on whether the action of hanging from the bar and preventing a ball from entering the net while doing so, would "be considered an offence of unsporting behaviour leading to an indirect free kick for which the [player committing the offence] should be dismissed" (for denying a goal) or not.If the hands are used, law 12 specifically covers it. Your email clarifyes if it also covers goal keepers.
The question is if it is DOGSO when crossbar is used for lift and a goal is denied using a body part other than the hands/arms.
The reply was that stopping the ball entering the net while hanging from the crossbar would be considered as an act of unsporting behaviour punishable by an IFK (and a sending off offence because it denied a goal). As far as I'm concerned, that principle would apply whether the USB involved a keeper using the hand or an outfield player using a different body part.