How to change custom page layout in Magento

There are few steps to apply custom layout to a page. I have describe here how change page layout using xml. This is a process of

create custom page layout in magento

.This custom layout is show also show in admin panel In generally, page template is set under

<reference name="root">

For set temptate ,mostly using


<action method="setTemplate"><template>page/empty.phtml</template></action>

and Mark root page block that template is applied

<action method="setIsHandle"><applied>1</applied></action>

Suppose i am changing template   in checkout cart page:

<checkout_cart_index translate="label">
 <reference name="root">
<action method="setTemplate"><template>page/2columns-left.phtml</template></action>
 <!-- Mark root page block that template is applied -->
 <action method="setIsHandle"><applied>1</applied></action>
</reference>
 </checkout_cart_index>

How to apply  Custom page layout handles in layout in magento shwoing here 

 <custommodule_cms_index>
<!-- Custom page layout handles -->
<reference name="root">
<action method="setTemplate"><template>page/2columns-left.phtml</template></action>
 <!-- Mark root page block that template is applied -->
 <action method="setIsHandle"><applied>1</applied></action>
</reference>
</custommodule_cms_index>