Adminhtml uses the same theaming mathod as the we do on frontend. We need to do two things
1. We need to only declare a custom template theme for your installation in module config.xml:
Add following code in -> app/etc/config.xml
2.Then you need to create directory “custom_theam_name” in app/design/adminhtml/default/custom_theam_name
Now you put you file/module folder Like.