---QUOTATION--- Not without the SDK. ---END QUOTATION---
Maybe not. In theory all you really need is the level geometry from SHOC and any files associated with it. Then just copy the files to CS, and modify one of CS level changers to take you to the old map instead of where it normally goes. Or even add a few new level changers attached to the new level. Assuming you know what you're doing with the level changers and have all the right files for the old level it shouldn't be to hard...
Unless GSC went and changed the way CS reads level geometry, making everything I just described useless.
"He who fights with monsters should look to it that he himself does not become a monster." - Friedrich Nietzsche