What's the best way to remotely summon independents

[Bananadine]

I'm trying to add a spell that'll let a player remotely summon an independent army. I'd like that army to try to take over whatever province it lands in and then stay in it thereafter, just as many randomly appearing armies of barbarians, knights, and Boguses do. I was surprised to learn that this is a difficult thing to do... at least, for somebody who only knows the basics of the mod system. Remote-summoning spells are pretty ordinary, but they always seem to produce units that belong to the caster's nation, or units that belong to Special Monsters.

I found one way to do this, anyhow: Hijack the spell Monster Boar, which seems to be tied to a hardcoded event, rather than to any general summoning system. I changed the spell's casting requirements and made the boar non-stealthy, and the job was done. I guess I could change the boar into whatever kind of creature I wanted. But... that'd hurt Pangaea. Also, I don't know how to change the message that comes with the spell, which still refers to a vengeful boar.

I'd like to just make a new independent-summoning spell of my own. Is there a better way?

If I have to hijack a spell like Monster Boar, can I at least choose a different spell? I couldn't think of any other Monster Boar-like spells, but maybe there are some. It would help a lot to have a few choices, because then I could just hang my mod on a different spell with each new game, according to which nations were unused in that game (so that nobody would be stuck with a slightly weakened Pangaea or whatever).

Can I change the text associated with the boar event?

Can I make a spell that invokes the Monster Boar effect in such a way as to produce multiple monsters? It'd be okay if multiple messages were also produced.