Terrain Impassibles doesn't work.

I've been using the SDK Modcomp, Mountains, back to service, which allows movement on peaks. I am trying to make it so that units can not move on peaks until they research a prerequisite tech, through terrain impassible, like ships can't move through the ocean until Astronomy. However, It doesn't work. My changes show up in the civilopedia, but in game, I still can move over the mountain... I have some screenshots to show it. Are the terrain impassibles broken?

Screenshots:
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I guess, canMoveImpassable just overrides that.
Because a terrain, which you can't move on, is impassable (no idea, how it's in the code, but i would say that from the logic).

I think that's becauase even though Peaks are listed as a terrain in TerrainInfos they aren't really a terrain. Along with Ocean, Hills, and Plains they are technically a "PlotType". Look in many map scripts and you will see that these are a separate thing entirely. In my FutureMod (as does TheJ in his MarsNow) I use the hill skin for peaks (since mountains on the moon and mars won't have snowcaps) and you can see that peaks retain the terrain of the underlying terrain, just like hills do. Thus you can't do what you are trying to do by treating them as a terrain type. Your best bet is to simply have a different unit, identical to the first in every way except the unitname and unitclass are different and it can move impassable and becomes available with a later tech. You can thus build it later or upgrade to it for a nominal fee.