Set Template in handle in magento

Question

I am using one step checkout and shipping_method.phtml responsible for showing the shipping methods.so now i have 2 more modules which both have shipping_method.phtml each.so i need to show either shipping_method.phtml from Module A or Module B depending on the shipping country.

so i wanted to update handle called in that i will be updating the handle with module A or B depending on the condition statfication which just updates the setTemplate file either from A or B.

Please Help me how to achive this.

<a_onestepcheckout>
    <reference name="choose-shipping-method">
        <action method="setTemplate">
            <template>a/l/onestepcheckout/shipping_method.phtml</template>
        </action>
    </reference>
</a_onestepcheckout>

<b_onestepcheckout>
    <reference name="choose-shipping-method">
        <action method="setTemplate">
            <template>b/l/onestepcheckout/shipping_method.phtml</template>
        </action>
    </reference>
</b_onestepcheckout>

// either a_onestepcheckout or b_onestepcheckout depending on condition
<onestepcheckout_index_index>
    <update handle="a_onestepcheckout" /> or <update handle="b_onestepcheckout" />
</onestepcheckout_index_index>

Answer 1

I don't think you can load a conditional layout handle from the xml.
You will have to do this in an observer.

Use the event controller_action_layout_load_before.
Something like this:

public function addSomeHandle($observer) {
    $action = $observer->getEvent()->getAction();
    $actionName = $action->getFullActionName();
    if ($actionName == 'onestepcheckout_index_index') { //if on your desired page
         $layout = $observer->getEvent()->getLayout();
         if (CONDITION GOES HERE) {
             $layout->getUpdate()->addHandle('a_onestepcheckout');
         }
         else {
             $layout->getUpdate()->addHandle('b_onestepcheckout');
         }
    }
}