I'm using Revit MEP and I have pipes that are underground, when exported to auto cad they look like anyother pipe. If I was able to change the style of the pipe I could assign that style to be a specific layer in the export so I wouldn't have to later move them and all their parts to their own layer. The best way for this to work would to be able to set a ceiling, and anything below that ceiling would be one object style/sub-catagory and anything above would be another object style/sub-catagory. I don't think this is possible in REVIT, but I also don't understand how REVIT wouldn't have this option. Could someone help me out and tell me if this is possible? Better yet, a way to make it work.
The only way I can immediately come up with is to use a Layer Modifier to the Piping Categories, and assign an override to the particular Modifier. For example, if you have a separate Piping System for Underground Piping, you could add the {System Name} Layer Modifier to the Piping Categories and then you could assign a Layer/Color override to that Underground Piping System, listed towards the bottom of the Layers tab (in the Modify DWG/DXF Export Setup dialog) under Modifiers > System Name. This may take a bit of playing around, but you should be able to get what your looking for in some way.