Hook into register_sidebar
and change the name after the sidebar was registered.
Example:
add_action( 'register_sidebar', function( $sidebar )
{
global $wp_registered_sidebars;
if ( 'Main Sidebar' !== $sidebar[ 'name' ] )
return;
$id = $sidebar[ 'id' ];
$sidebar[ 'name' ] = 'Master';
$wp_registered_sidebars[ $id ] = $sidebar;
});
There is no need to unregister the original if you want to change just the name.
You can change other properties too:
description
class
before_widget
,after_widget
before_title
,after_title