This plugin allows you to customise the labels of a Custom Post Type.
It doesn't allow you do other things such as changing the Custom Post Type's slug.
If a theme hard-codes the names/labels of the custom post type (for example in it's breadcrumb), then this plugin is unable to override it.
The plugin overrides the custom post type's registered labels, but it is still up to the theme to correctly display a CPT's label(s).
As an example, recently I found that some WooThemes were hard-coding the custom post type name on custom post type archive pages. I contacted WooThemes, and suggested that their archive templates use the post_type_archive_title() function instead, and once they made that change then the customised CPT label was used on the archive page.
I hope that helps.