If ever I will change or doing some amendment of the first above mention would that affect to any future updates of the theme and in the plugin? Modifying or renaming the entire fields of the Billing and Shipping details page?
we recommend you to make all changes to theme files only in child theme.
This will prevent you from breaking your site or losing customizations on theme update.
Read here for more details: codex.wordpress.org/Child_Themes