WP Template Overrides allows you to quickly and easily override any template file in any theme you currently have installed.
Once the plugin has been activated, navigate to Tools -> Template Overrides.
Once on that page, select "New Override" from the tabs at the top.
After entering the "New Override" page, select theme you need to override, then select the file you wish to override and after the content has loaded to the editor, press save to create the overide. Pressing edit at any time from the list overrides page will enable you to edit the template override.
If you make a mistake in your PHP syntax, and press save, it will cause a blank white screen or a displayed error on that page of your website. You will still be able to access wp-admin to correct the mitake.
The file editor included has some basic PHP syntax checking, so watch for the little red X on the left before you save.
You can log a ticket in the WordPress forums by clicking the support button above, or if the matter is private and confidential, please drop me a line at Tiger Strike Media