Captain Sim Mig Stick Assignment question

In FS9; I'd like to assign the HUD color change function on the Captain Sim
Mig 21 to a stick button. The assignment as supplied by Captain Sim for this
function is a keyboard assignment Shift+ i.
In the FS9 control assignments, there is no Shift + i assigned to anything.
Is there a way to assign this key function to the stick, or must it remain
the way it is; only usable as the key assigned already but not listed
anywhere?
Thanks much
Dudley