The changes have to be done by coding and not using any plugins. We don't want the website's performance or responsiveness to be changed.
Changes will be like changing the UI of some pages, adding custom functionality on pages and dashboard, adding additional options in registration forms, improving the dashboard of WordPress (Hiding many options and showing only a few), adding custom options on pages. A detailed list of changes will be provided.
Only message if you have code-level knowledge of WordPress.