I think that yve is trying to copy the custom property of his part into a custom property of his plan, the ones that are in the "Summary information" dialog box and I don't think it's possible other than by macro, the equivalent of what Mycad tools surely do.
The advantage is that the "Description" property of a SW document can be displayed from Windows Explorer. And when you look for the plan of the engine mount or the washer among a list of documents named "plannumber.slddrw", you don't necessarily want to go digging through the nomenclature every time. For the parts that are named rondellebidule.sldprt, I chose to repeat the nomenclature marker in "Designation"
I have Mycad and I created this link function. Simply, I will generate my plans automatically with integration (just put 3 views on the right background and save in the right name), before sending them to subcontractors who will do the quotation. And these subcontractors don't necessarily have myCAD.