Is it possible to change a template and change all the pages?

I made a template with the Muffing Builder for many pages. I have almost 20 pages. I'm wondering if I could change the template that I made and as a result all the pages change.
I check it and I can't do this with this templates. I have to modify the template and afterwards import and replace the content of all pages but I have changed some content in each page so I need to use the Muffin Builder as the widgets in Wordpress.

thanks