Switching from ranged to melee

o_O I was wondering if there is a way to switch a unit from ranged attacks to melee attacks when they get within a certain range of a unit.

i.e. a troll axe thrower is ranged up till about a distance of 200 and then switches to melee attacks.

I've done a little testing with this, mostly attempting to use the minimum attack distance, but it didn't work because the minimum distance applies to both attacks.

I think your only chance would be to use an Orb ability to change which attack is enabled, running on a trigger that fires when the unit gets close to another unit.