[PvK]

For pretender creation, you can control what pretenders are available to each nation. You can also give them very high costs to add paths. And if you want them to have choices for some paths but not for others, you can duplicate some pretenders but give them different starting paths.

If you're willing to make your scenario in the form of a saved game, you could also start with some domes cast over some areas to protect against teleportation.