Is it possible to add new Attributes or modify existing ones (like their name). Don't think there's quite as much as I'd like to work with.

Also is it possible to Give a behavior or ability to a unit that makes it take a certain % less damage from units with specific attributes?

You should be able to rename attributes in the text module.

but you can't create any? :\

I don't know because I'm using triggers to do that sort of things because I can easily pile other functions onto it...
But you would need to trigger all damage to do things correctly then.

But I haven't tried the inbuilt attribute stuff, yet.

Not at the moment. You can make custom behavior attributes, but they work differently.

Yes. In the Damage Effect, you can set how much more or less it will do to a unit based on if they are Light, Heroic, etc.

That only deals with the attacking unit's point of view.

It'd be much easier to have one specific unit take reduced damage from certain kinds of attacks and units with attributes (such as from a melee light unit) if you could just give it a behavior for that.