Terrain passability modding

[Core Xii]

Is it possible to make desert plots impassable to land units by default, then have a tech that makes them passable? (by e.g. giving units a promotion, similar to embarking)

 

[DoctorMcGann]

I'd like to know this too, it would be really useful for an Oz scenario.

 

[PawelS]

Make a promotion like PROMOTION_OCEAN_IMPASSABLE_UNTIL_ASTRONOMY, but in the UnitPromotions_Terrains table, use Desert instead of Ocean, and the tech required to pass Deserts instead of Astronomy. And give this promotion to those land units that shouldn't be able to pass deserts without the tech.