Brush Panel Transfer Mode Toggle

The problem you will have is that the presets will only be of use to one brush.

This will toggle between to presets.

#target photoshop;
var PT = $.getenv("PanelTransfer");
if(PT == null || PT == "OFF"){
    $.setenv("PanelTransfer","ON");
    selectBrushPreset("Brush Panel Transfer ON"); //Name of brush preset
    }else{
     $.setenv("PanelTransfer","OFF");
    selectBrushPreset("Brush Panel Transfer OFF"); //Name of brush preset
        }
function selectBrushPreset(preset) { 
var desc = new ActionDescriptor();
var ref = new ActionReference();
ref.putName( charIDToTypeID('Brsh'), preset );
desc.putReference( charIDToTypeID('null'), ref );
executeAction( charIDToTypeID('slct'), desc, DialogModes.NO );
};

A script can  be triggered with a shortcut  using edit keyboard shortcuts. Actions can be assigned a f key short cut and that actions can use  scripts.  So yes a script can  run  with a key.  A script can be programmed  to toggle between selecting presets on and off.