You don’t need to add these snippets to CS plugin. I took them from its source code to show you the possibility to change ‘manage_options’ to any other user capability.
If do not change that, just grant ‘manage_options’ capability to shop manager. It will get access to the ‘Snippets’ admin menu. Also it will get access to all other admin menu items, protected by ‘manage_options’, like ‘Settings’ for example. You can block them using “Admin menu access” add-on included into URE Pro.