You can convert any procedural terrain into a heightfield by plugging its output into the Shader Input port on a Heightfield Generate. Then you can run any heightfield operations you want on it, including Erosion. Keep in mind, though, that this process computes the terrain at a specific, fixed resolution (adjustable in the heightfield generate settings), so you lose the benefits of "infinite" procedural detail. However you can always add more procedurals on top afterward to get more small-scale procedural detail.
- Oshyan