WordPress Theme Customization

We have a WordPress theme with many customization and most of the changes have been made to a child theme, but some features have been customized by directly touching the main theme code. We want to update to the latest version of the theme and add the customization without losing custom functionalities. To update the theme in the future without the risk of losing personalizations, I would like all the changes to be made to the child theme. I need to add the following new customizations: 1- Autofill a field of a form with the data of other fields of the same form. 2- Autofill a price field by calculating the amount of another field and convert according to the currency exchange using functions of an existing currency converter plugin on the site. 3- Create a switch button to display the results page view in the list view or map view. (There is already a map view on another page, the code can be adapted and used). Attached PDF with details Thank you for your interest!