Hi,
yes it's possible, this is question about Joomla 2.5/3.1 feature called "Styles" .
Just use "Duplicate" button in Template Manager. It makes a copy of the selected template style. The copy is created immediately and is given the same name as the original but prefixed with "Copy of" and/or suffixed with a number (eg. "(2)") so that it can be distinguished from the original and any other copies.
Then inside GK Template choose another Style from list, afterwards use "Menu assignment" - this section contains all the menu items configured in your Joomla! website. To apply the current style to a menu item's corresponding web page, check the box next to the menu item. At the end [Save] button.