There are several technologies to create websites. Some of them are adaptive and responsive design.
New version of Adobe Muse allows to create either adaptive and responsive websites.
Breda theme was created in adaptive layout, before responsive features in Muse.
Those two methods are completely different.
1. Adaptive design uses static layouts based on breakpoints which don’t respond once they’re initially loaded. That’s means you need to create website design for desktop, tablet and mobile separately. This method allows you to create different designs for each device.
2. Responsive websites respond to the size of the browser at any given point. No matter what the browser width may be, the site adjusts its layout in a way that is optimized to the screen. This means you need to create breakpoints for different sizes you need and adjust the design.
In your case, when you make some changes in desktop layout you need to make the same changes in mobile layout as well.
The same way when you create responsive websites you need to adjust your design for every breakpoints in order your website look as you want.
P.S. Create website in adaptive layouts is much easier to my personal opinion. You can continue modify the template in adaptive layout or switch to responsive, add breakpoints and adjust the design.
I hope this helps.