In Active-HDL, do the following:
Open the .bde file that you need to modify.
Select File | Save As from the main menu and save the file with a different (new) name.
Select Diagram -> Code Generation Settings.. from the main menu.
In the Code Generation Settings window change the entity/module name in the Entity/Module field to a desired name. Click OK.
Modify and save the file (if needed).
Compile the file. Once done, a symbol will be created for it automatically.
Open the Symbols Toolbox and drag the new symbol into your diagram.