yeah, electronic EQ is a very different thing from physically disconnecting a component.
it would probably be easy to disconnect the horn circuit without affecting the rest of the speakers, since like most production bass cabs it likely runs the speakers full-range, just adding the horn "on top".
it could be as easy as pulling a connector clip or two off of the inside of the jackplate (then taping them up so they don't touch anything).
Guitar Repair Gnome
Alpha Music, VA Beach