To rename block in AutoCAD, you can use rename command. This command is also can rename the other object like block, linetype, material, and dimension. But you only can rename individual object in a time.
AutoCAD How To Rename Block
1. Make sure block already insert into drawing
2. Type rename (enter), will be appear rename dialog box
3. Choose block on name objects, and select block name on items
4. Set new name on rename to column and click rename to
5. Click ok to finish
6. To save block, you can use Wblock command