Gallery layouts are determined on a gallery by gallery basis. This means that within one collection of galleries or one template instance you can have each gallery using a different gallery layout.
How to assign a layout to a specific gallery
1. In the galleries tab in the template admin click on the current gallery layout.
2. Select the layout you want to use for the that specific gallery
3. Once a new layout has been chosen the new layout is instantly applied to the front end of your site.