Hi, Louise,
First, you can edit (customize) module's master-slide at any time. After that you can save your template in My Templates section (using Service menu).
Second, if you want to change one template to another - switch right panel into Templates view, select desired template and drop it onto the module window. Additional master-slide will be added to module. In the Slides panel select all the slides you want to use new master-slide, right-click to get context menu, select Master-slide option and select desired master-slide icon. All selected slides will get new master-slide.
Hi, Louise,
First, you can edit (customize) module's master-slide at any time. After that you can save your template in My Templates section (using Service menu).
Second, if you want to change one template to another - switch right panel into Templates view, select desired template and drop it onto the module window. Additional master-slide will be added to module. In the Slides panel select all the slides you want to use new master-slide, right-click to get context menu, select Master-slide option and select desired master-slide icon. All selected slides will get new master-slide.