When you say in code or data, do you mean some spot in the engine that we dont have access to? Or is there a place in the editor somewhere?
When I said 'data' I meant the entries you can adjust in the stats editor. These you can access, but only within the limits of the variables defined there.
When I say "code" I meant that these things are part of the programming of the engine itself. To change these (or at least, to change them in the same way they work in the game), you'd have to build an entirely new binary.
That said, if you're not too concerned about systems like the AI knowing what it is your changes do, you can indeed use script to work around the existing systems like LaughingLeader suggests.
But it should explain why you don't see scripts defining how skills and abilities work - that's not normally governed by script.
More relevantly to your problem: Statuses have an OnDie action, which can trigger a projectile skill (as if a projectile impacted at the location of death), which in turn can summon a character.
Those are limited by the maximum amount of summons the character has however.