I have same problem (smaller site but many contour points) but may have figured out a rather unwieldly workaround.
Before editing the Toposolid in the Orig file, make sure to make a copy of your project (Temp Topo file) and have the same view opened in it.
Go to the Orig file and edit the Toposolid. Once editing is complete:
1. Select the Toposolid in the Orig file.
2. Copy/Paste it into the Temp Topo file (Aligned to Current View).
3. Then save the Temp Topo file (with new Toposolid).
4. Next, CTL ALT DEL and force closing of Revit!
5. Open Revit and re-open both the Orig file and the Temp Topo file.
6. Select the (old) Toposolid in the Orig file and DELETE it.
7. Select the (new) Toposolid in the Topo Temp file.
8. Copy/Paste it into the Orig file (Aligned to Current View).
9. Finally save the Orig file with the New Toposolid.
Hopefully there is a better solution around somewhere.