I see same code under following dir: (4.3.5 version)
What is the reason for this? Why can't there be a single copy of code?
If I want to add a new add-on, do I need to update files in both of above dir?
The design/themes directory contains themes which are used in the store. The var/themes_repository contains original files of themes. For example when theme or add-on is reinstalled, all template files are taken from this directory of CS-Cart installation.
An add-on can use this directory to store its template files. For more information, please refer to the following articles: