Wordpress - Is there way to rename user role name without plugin?

function change_role_name() {
    global $wp_roles;

    if ( ! isset( $wp_roles ) )
        $wp_roles = new WP_Roles();

    //You can list all currently available roles like this...
    //$roles = $wp_roles->get_names();
    //print_r($roles);

    //You can replace "administrator" with any other role "editor", "author", "contributor" or "subscriber"...
    $wp_roles->roles['administrator']['name'] = 'Owner';
    $wp_roles->role_names['administrator'] = 'Owner';           
}
add_action('init', 'change_role_name');

http://www.garyc40.com/2010/04/ultimate-guide-to-roles-and-capabilities/

Actually, there are many ways to achieve that:

With pure php and mysql you can edit the serialized entry in the db. Indeed, Wordpress stores the serialized array of roles in wp_options table.

So:

1. Fetch the serialized array:
   SELECT option_value as serialized_string FROM wp_options WHERE option_name = 'wp_user_roles';
2. Unserialize the string – php: $rolesArray = unserialize($serialized_string)
3. Change the role name – php: $rolesArray['role_key']['name'] = "New name"
4. Serialize back the array – php: echo serialize($rolesArray)
5. Replace the db option_value content with output from the previous point

If you feel confident with Wordpress, you can even use the embedded Wordpress REPL in wp-cli to fetch the stored value with get_option('wp_user_roles') and then use update_option to update it.

And (always) remember to backup the db before options manipulation ;)

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Otherwise, if you don’t care about role_key value…

…it’s very easy to achieve that with wp-cli:

1. duplicate the existing role – $ wp role create new_role 'New Role' --clone=old_role
2. delete the old one – $ wp role delete old_role
3. then associate new_role to the user(s).
4. eventually repeat step 1 and 2 until old_role = new_role

A simple solution would be to just add a user role using add_role, that way you can name it whatever you want and add whatever capabilities you want. http://codex.wordpress.org/Function_Reference/add_role