You may, but be carefull!
THIS is the single Dopest thing autodesk did inside C3D
Drag that Material Column WIDER than your desired Material name or it will NOT let you key it all in there.
So first you add your pipe size to the part family,
And the your Rt-Click and edit it
Drag the Column open wide
A subtle double click action will highlight the material value.
Type in your new value.
It will now be available for all pipes.