Create sub-administrator role that can do everything except use or see the code editor

Your code isn’t working because WordPress deprecated user levels in version 3.0 (June 2010).

What you want to do is create a plugin that upon activation, creates a new role for the owner of the site that is a clone of the administrator role, but cannot edit plugin or theme files. Those capabilities are edit_plugins and edit_themes respectively.

Then, upon deactivation, you want to reassign the owners into the administrator role. This way, they can fully regain control of their website by simply deactivating the plugin.

/**
 * Plugin Name: WPSE 264483
 */

//* On activation, create an owner role that can do everything but edit themes/plugins
register_activation_hook( __FILE__, 'wpse_264483_activation' );
function wpse_264483_activation() {
  $administrator = get_role( 'administrator' );
  $owner = clone( $administrator );
  unset( $owner->capabilities[ 'edit_plugins' ] );
  unset( $owner->capabilities[ 'edit_themes' ] );
  add_role( 'owner', 'Owner', $owner->capabilities );
}
//* On deactivation, re-assign all owners to administrators and remove owner role
register_deactivation_hook( __FILE__, 'wpse_264483_activation' );
function wpse_264483_deactivation() {
  $owners = get_users( [
    'role' = 'owner',
  ] );
  foreach( $owners as $owner ) {
    $owner->add_role( 'administrator' );
    $owner->remove_role( 'owner' );
  }
  remove_role( 'owner' );
}

I’ve enabled a similar plugin for clients upon request, but I think it’s a bad idea to do so without their full knowledge and consent. It is their website after all.

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