I think the OP is talking about the opposite scenario.
He wants to bump the gain on the Mesa, and use the FDeck as an attenuator to keep the output volume under control.
My only concern would be that if he pushes it too hard, he might overload the FDeck's input, and damage his HPF.
Two options: PM Francis and see what he has to say about it, or try tentatively pushing it to see how soon the HPF starts making nasty noises.
Dingwall ABZ-5 : Squier VM Precision V : Shure PGXD Wireless : Zoom MS-60B : GK MB110 combo : GK MB800/MB200 heads : AudioKinesis TC112AF