The only work around I've found is to reduce the total size/area of the toposolid element which is being edited. This is not ideal, but in my case the full site toposolid which was about 50 acres now only serves as the background existing topo surface, but I don't modify this one. This site is separated by a winding road, so I asked the civil engineer crop the topography cad file down the centerline of the road into groups of 4-5 typical residential lots at a time. I then generated a toposolid of each smaller area overlaid on the full site 'existing' topo.
I now only modify the points of the smaller toposolid elements, rather than modifying the element which makes up the entire site. When modifying points of the smaller toposolid elements, it has so far stopped crashing and freezing so it would seem that revit is just not able to handle the calculations of changing a larger component with so many points. The reason I went this route vs the 'simplify toposolid' to reduce total points is that I had already tried reducing the points 3-4 times, but it never worked without crashing during modifications, and was getting to the point that it was so simplified that the nuance of the site was being lost.
If you can break up your overall site into smaller chunks before modifying those piece, that has at least helped me continue to work. This is definitely not an ideal solution, but it may be a temporary work around until the tool is redesigned in a way that doesn't crash the program.
