I belive ( someone confirm please )
You can manipulate it, but it loses ALL intelligent data associated with it, and it is one way. Basically you break the drawing to manipulate it in regular Autocad.
The blocks etc transfer, but it will no longer be classified as a pipe - no click dragging, attaching other pipe fittings etc.
"Do or do not... there is no try"
A clearer definition of "manipulate" would help.
One of the core concepts of the AutoCAD vertical products (like Plant3D) is having intelligent/data-bearing objects which can be manipulated by that specific software while still capable of being viewed or inspected in basic AutoCAD or other DWG-using software (like Navisworks or TrueView) via object enablers. They are rarely capable of being changed outside of the actual software for both programmatic and cost reasons. So you may be able to inspect a limited amount of information off of the objects, but I doubt you would be able to make any changes, at least not without compromising the integrity of the data.
If you are going to fly by the seat of your pants, expect friction burns.
Adopt. Adapt. Overcome. Or be overcome.
How about stairs for example: could a person draw stairs in Plant 3D using the stair option, then take those stairs into regular AutoCAD and be able to slice oor strech them as needed?
the structural elements in plant are NOT intended for detail design, its a piping program
They are there for doing proposals and for giving to a proper structural program for detail design and documentation, thats why you get ASD and Revit with it...do the structural design in Revit/ASD, do the P&ID and Piping in plant3d, do the coordination and clash detection etc in Navis.
You can do it your own way,
If its done just how I say!
[Metallica:And Justice For All:1988]