Hi,
Use FORMAT>RENAME command to rename the existing block where using SaveAs tool in the block editor will create a new block based on the existing block. Use either Refedit or Block Editor to add features to existing blocks. {Refedit to add geometry while in place, which allows to add geometry while in place and add other objects in the drawing to the block. Use Block editor if you are adding new geometry or dynamic features.
Hope this will help you in some sort.