Thank you all for your responses. I asked a couple more people and finally found a solution, although it's not ideal, it's still better than nothing.
The camera responsible for the zoom (for heroes) is located at this path: ArenaObjects\_(CombatCamera)\Heroes. Let's take the Necromancer folder as an example. It contains the files Spell_Cast and Attack.
In this file, in the "creatures" parameter, we specify the paths to our new hero CreatureVisual files.
Now we have a standard camera zoom for the Necromancer's spell cast for all our new heroes.
This solution is not ideal because, in my specific case, I am using new models, so sometimes the camera cuts off part of the visuals, but this can be fixed by creating new cameras for the spell casts:
The Necromancer has 4 cameras for spell casts (I don't know what the difference is, other than the values inside the camera). In these cameras, you can change the values, thereby adjusting them to the new hero models
This should also work for RangeAttack; I'm going to try it now :)