How to Clone a WordPress Theme
There are times when you need to clone a wordpress theme. Suppose you want to customize the template of WordPress’s default Twenty Thirteen theme. You should not edit the template files of the Twenty Thirteen theme directly, just like you should not edit WordPress core files. Because at the next WordPress update, it may overwrite your template customizations.
What you want to do is to clone the Twenty Thirteen theme and give it a new name. Then you can make customization edits to this new theme.
1. In your wp-content/themes/ folder, copy the twentythirteen folder to a new folder called twentycustom. We will call our new custom theme “TwentyCustom”.
2. Within your new twentycustom folder, find the style.css file and edit the theme name to be “TwentyCustom” . This line enables WordPress to find your theme. You might want to alter the description and other properties in the file as well.
3. Now when you go to Appearance -> Themes in your dashboard, you will see your new TwentyCustom theme. If you want to change the theme thumbnail image, it is the file screenshot.png in the twentycustom folder. Click “Activate” to activate your new cloned theme.
4. Now you can go make whatever edits you want in the theme files within the twentycustom folder without worry that WordPress updates would overwrite it.