New slide
Ctrl M
Copy Styles
Ctrl Shift C
Ctrl Shift V
Group & Ungroup
Ctrl G
Ctrl Shift G to Ungroup
Duplicate Slide
Ctrl D
Slidemaster
Alt W M
If you edit this subslidemaster, it will make that change to all slides with that same layout.
Editting the main slide, slidemaster, will make that change, e.g. background colour, to all slides