Terrain shaper manipulation was added in 21w43a. However, it has no effect on the terrain, due to the fact that the terrain shaper in the noise settings is not used. I have attached a sample datapack; the terrain shaper in this pack has been gutted with almost all values deleted. The expected result is essentially blank and boring terrain shapes, but normal Minecraft terrain generates instead.
- Add the attached datapack to your world
The terrain shaper didn't affect the terrain
The the terrain should be affected by changes to the terrain shaper.