[douglas]

1) No. The existing abilities allow for a lot of possibilities, but this isn't one of them and you can't make new ones. Sector damage would be the closest you could get without using an AI player, but that wouldn't be a one-time event. If you set up an AI/neutral player on the planet you could have that player build a bunch of weapon platforms. I can't think of any other way to do it.

2) As you've already noticed, the free techs from colonizing it are trivial. The guardian, however, is not. All ships must belong to a player and must be built at some point during the game. For the guardian to exist, an AI or neutral race must have built it. It is, however, possible to create an AI race that will build exactly one guardian, keep it at its homeworld, and do absolutely nothing else.

First, you have to make all the components and the hull for the guardian. Make all of them require a "guardian race only" racial trait. Design the guardian so that it has no standard engines and is therefore incapable of moving around in a system, and give it a combat-only movement bonus instead. Then, design the AI race that will build and control the thing. In the ship designs file, put the design for the guardian as the one and only entry. In the vehicle construction file, tell it to build one guardian and nothing else. In the politics file, make it so the race hates everyone and will not accept any deals of any kind. I haven't done much AI modding myself so there might be something else I've forgotten, but that should result in an AI race that builds one guardian, keeps it home (it's actually incapable of movement outside of combat), and does not interact with other players except to defend itself when attacked. If SEIV has some fallback option for when the race AI files run out of things to build you may need to make the guardian require almost the race's entire production to maintain it, but I don't think that will be necessary.