YITH e-commerce plugin customization updated with doc. file

We would like to build an e-shop using Wordpress with YITH e-commerce plugin ([login to view URL]) that we need to customize it a little bit. The concept of the e-shop is "Rent a dress". In order to succeed on that YITH supports a nice booking processing system. The buying process will also be as it is by default. Actually, the renting process is the one that needs customization. The customization will take place mostly on the product page. We have chosen YITH as an e-commerce platform (WordPress plugin). The problem is that concerning booking products YITH delivers 1 number field for choosing the number of days you like to rent or book the product/service and a date field to start the reservation. What we really need is to have radio buttons for the duration which are going to be configured by the admin and will deliver options like 3days, 6days, 9days, etc and a date field as it is now. So the actual customization will be only for the duration which instead of having just a number field we would like to have pre-configurable radio buttons (3days, 6days, etc) It is also very important that this customization must be built in override files and not in the actual core files of YITH in order to be able to update it smoothly without any issues! Bellow, I am giving you an example of how YITH is functioning now (demo page) and another example of how we would like to customize it (an Actual example that our customer gave us) YITH functionality as it is now: [login to view URL]