[Endoperez]

Or making the land-freespawn Aquatic and water-freespawn non-amphibian.

There are ways to kill the freespawn, but both types of freespawn are used by other mechanics (undead by reanimation spells and strategic command, mad people by Imprint Souls) that can't be duplicated with the existing modding commands. So if you remove the freespawn, you also remove other features. Imprint Minds isn't that important, so it might be doable for LA R'lyeh.