I would like to know if there is a way to create a toposolid using RiR and assign subdivisions to it, but have the result be a clipped toposolid, not an unclipped one.
No, but I think you can achieve this result in a version other than Revit 2026. When doing this in Revit 2026, the subdivisions still overlap the toposolid. Versions like 2024 and 2025 create a layer over the toposolid, without cutting it. I amtrying to avoid this solid overlap in Revit 2026 (i.e., by cutting the solid — doing this manually, Revit creates these cuts where there are subdivisions automatically, but I would like to do it in Grasshopper).