To edit the 2D display of a symbol in X12 and prior versions You can now add the symbol with its customized 2D block to your User Catalog folder in the Library Browser by selecting the symbol and clicking the Add to Library edit tool.Close out of the CAD Block window to return back to your plan.In the Question dialog that appears, you can choose to replace instances of the existing CAD block with the newly modified version.
Make any other desired changes to the other CAD objects, then click Tools> Active View> Save Active View.