If you want to Set package and theme at run time in magento simply use this code snippet.
create one function ex. changeTheme('Theme-name'); and run this function with your requirement
add this function in your head.phtml after php start.
function changeTheme($themeName) { Mage::getDesign()->setArea('frontend') //Area (frontend|adminhtml) ->setPackageName('default') //Name of Package ->setTheme($themeName); // Name of theme }
enjoy :)