It is common that users want to add an extra object(s) in the middle of editing CTA project to AE. In CTA v.4.5, users are able to add extra items without overwriting the edited CTA project in After Effects. 
Here is the instruction for adding extra object(s) to your animated project in AE:

1. Add the extra object in the scene in Cartoon Animator (CTA).

2. Click on "Export to AE" button  , and re-export the CTA project. When exporting, select the original project and overwrite it. 

a) Cartoon Animator program will automatically export just the newly added object, and keep the original object files intact without overwriting.

That being said, if you modify your original objects, it won't be saved in the new Json file.

b) Please note that CTA program identify whether it's a "newly added" object or not by naming and file format. When the object is named differently, the program would identify it as a "newly added object".

3. Go to the current CTA project in After Effects, reload the overwritten Json file.
4. The newly added object will display on the top track of all layer tracks. Users can then adjust the layer accordingly.

NOTE: When exporting and overwriting the JSON file, please note that you shouldn't change the export render setting (for example,  the frame size, the frame rate, etc.)