**UPDATE**

After some more testing, it looks like I can't use Reposession at all. It's always blocked regardless of artifact presence.

Outdated:

If you try to use ALT's Repossession on a world that has been flagged as having an artifact (not THE artifact for Occupation Victory, just AN artifact, like Manifest Dominion), the ability is blocked and the message "Target cannot be the Artifact World" is displayed. I don't know if it's still blocked if the planet isn't "known" to have an artifact yet (I'm assuming yes, since this is how it works for the Artifact World). I'm hoping this is a relatively simple error to fix, like a typo in the property that's being examined.