You do know that Locust Swarm is actually a Summoning-type Spell ?
It spawns multiple of units around your Hero and damage any nearby enemy unit within its contact.
You know how it deals the damage ?
It comes from the unit itself, yes, it's a unit, the name of the unit is "Locust" (search for it in Object Editor).
Ok, once you have found it, you just need to change its damage according to your Hero's INT, right ?
First, change the Locust's Damage Field to these:
Combo - Attack 1 - Damage Base: 0
Combo - Attack 1 - Damage Number of Dice: 1
Combo - Attack 1 - Damage Sides per Die: 1
By changing to these setup, your Locust now will deal damage of 1-1 (that is the minimum damage for it can get if the Hero's INT is 0).
Next, you would implement a bonus mod system, which will modify your unit's attack damage to your will.
But first, I need to solve this first:
http://www.hiveworkshop.com/forums/world-editor-help-zone-98/linking-units-225630/#post2245138
Once I solved that, I can do this for you.
EDIT:
Can the Hero be created more than 1 unit at a time in that game ?
Can the Hero be controlled more than 1 players at a time in that game ?