In answer to your questions:
1. Yes you can disable registrations easily from within the WordPress admin dashboard.
2. When a user registers as a job seeker, they will see the option to add a resume via their dashboard, changing this to something more prominent on the homepage would require customization on your part, but can be done.
3. Our themes are not encrypted, so you are free to make modifications if you wish.
4. As these are default links, it would require customization to remove them.
AppThemes doesn't offer customization services, however we do have a
certified partners page where you can find developers for hire. Thanks.