No. You are not allowed to modify any of our Plugin code. Even if you modify, the update will completely erase the modification you made and it’s completely not recommended. We Won’t provide any support if you modify the code to change the functionality of our Plugin.
In case if you want to extend the functionality of Plugin, you should create a child theme for your parent theme and modify the code in functions.php file. This is recommended in case of utmost importance to extend the functionality of Plugin.