Modifying the default post from wordpress

This is not advisable to do. A lot of things in WordPress depend on having posts and pages acting as they are. You can change labels, but, changing other settings will very likely break something.

It is much better to create new post type, then messing up posts or pages.

Also, the function you used ‘register_post_type_args’ doesn’t exist in the WordPress, it is either part of some plugin you have, or it will throw errors. WordPress has ‘register_post_type’ function, but that can’t be used to modify parts of the post type.