Customisation Off WooCommerce Checkout

I need to modify a plugin to create a custom checkout for WooCommerce on Wordpress. The customers delivery price is determined by their postcode. This has already been set up using Table Rate Shipping. However, this price is increased by 50% if they choose delivery on a Saturday or Sunday. I had a developer create the code to do this on a plugin called "Order Delivery Date for Woocommerce", but I need the code to be applied to a new plugin called "WooCommerce Delivery Slots" - where they can also choose between a morning or afternoon delivery. Hopefully this should be copy and pasting the existing modifications and making some slight alterations. This is time sensitive and needs to be completed as soon as possible (tonight/tomorrow morning). I will be online constantly to answer any questions, help test and provide all necessary login details. Other things to note: They can also select Free Pick Up at no charge (already set up through WooCommerce). There needs to be a pop up alert if they select Sat or Sun for Delivery (already set up with old plugin). I need it built in a way that I can update the plugin without breaking the customisations. I will need all modifications emailed to me so I have a hard copy at the end of the project Thanks for your time Chris