you cant effectively change his range. you have to be creative. possible ways:
1. use an orb
he already gives melee units ranged attack. i dunno if you can make it target ground though.
2. use metamorphosis
dunno if its the name exactly, i mean the ultimate of the NE demonhunter. he gets ranged, though with some other effects, you gotta try if you can change them all.
3. give your hero 2 attacks
and set different allowed aims for them (like mechanical /organical)
then change the type of all enemy units to type mechanical or w/e by this trigger.
easiest way probably, but then you cant use mechanical/organical types for any other use.
so far