<?php
if(isset($_GET['view']) && $_GET['view'] == 'onlinestore')
{
Mage::getDesign()->setArea('frontend')->setPackageName('default')->setTheme('modern');
}
else
{
Mage::getDesign()->setArea('frontend')->setPackageName('default')->setTheme('epovmobile');
}
?>
http://magento.stackexchange.com/questions/2920/how-to-add-desktop-version-and-mobile-version-link
Write below code in action to set Package and theme for the action
Mage::getDesign()->setArea(‘frontend’) //Area (frontend|adminhtml)
->setPackageName(‘default’) //Name of Package
->setTheme(‘modern’); // Name of theme
You may write the code in layout handler to set theme
<reference name=”root”>
<action method=”setTheme”><theme>modern</theme></action>
</reference>
Change page layout
<reference name=”root”>
<action method=”setTemplate”><template>page/1column.phtml</template></action
</reference>