Point a template at another

We had a general page template but have some 20k pages that are using this layout. We have another layout that we’ve gone to. Without having to change all those pages or have two of the same template. Is there a way i can point Page to my Sibling_menu template?

I solved this. What i did was create a snippet. The dropped all my layout code in there. This way I can just drop the line

<?php snippet('siblingmenu') ?>

into any template but only have to edit one file.

The cleanest solution would be to do a batch rename of your content files, there are several tools available to automate this. But your snippet solution works as well of course.