Change Default Custom Fields Metabox Name on cctm plugin

Try using this example from the WordPress Codex:

add_action( 'add_meta_boxes', 'myplugin_add_custom_box' );

function myplugin_add_custom_box() {
  add_meta_box( 
    'myplugin_sectionid',
    __( 'My Post Section Title', 'myplugin_textdomain' ),
    'myplugin_inner_custom_box',
    'post' 
  );
}