Customize an existing joomla extension to add features

The joomla extension is : Rs membership, the selected freelancer will customize to add the following requirements : The system will have a chat system only available for paid clients. The system will show in text formt the privileges a client have (phone calls, chat sessions, etc.) This will be modifiable by an admin user The system will have an appointment system in order to setup appointments with admin, viewable only for paid clients. Validating if the client have free appointments available in their membership. I will provide with required extensions.