Create a new theme that contains any master slide changes you’ve made to the current theme.
Choose File > Save Theme.
Type a name for your theme.
If you added sound or movies that you want to include in the theme, select “Copy audio and movies into theme.”
If you don’t see this checkbox, click the disclosure triangle to the right of the Save As field.
Saving media files with a document makes the file much larger.
Click Save.
Unless you specify another location, custom themes are saved in the Themes folder on your hard disk ([home]/Library/Application Support/iWork/Keynote/Themes). Only themes in this folder appear in the Theme Chooser. If you store your theme in another location, you can still open it (from the Finder) and use it to create a slideshow.