Change items given by resource dispenser

Hi, today i wanted to work on a plugin that will change the items given by a rock or a tree.
I was wondering if i can modify the containedItems in ResourceDispenser depending of the entity if it's a tree, or an ore.

 

Code:

void OnDispenserGather(ResourceDispenser dispenser, BaseEntity entity, Item item)
{
    Puts("OnDispenserGather works!");
}

^^ info is contained in Item that you would want to look at