This one is a doozy.
I started with an existing part to make a new part template. Under File / Properties I have set: the properties for Description, Material & Weight.for use in filling in this data in my drawings. It just so happens this original part was 6061 aluminum. I deleted the part extrusion and sketch, leaving me with a blank page, and then saved it as a new part template. As a followup, I did a test part with the new template. Regardless of material chosen or part dimensions, the mass tool says my part weighs 5.3 pounds, which was the weight of the originaal part. The File / Properties menu on the new test part says it's referencing the new test part for it's mass data yet will not display the correct weight of the part.
Nice!