SOTP Vintage Series
Main Motorcycle: '98 T595 Daytona
Join Date: Mar 2011
Location: Northern NJ US
Other Motorcycle: 2014 Ninja 1000ABS
I suspect in both instances, the bag brackets are attached to the rear subframe avoiding any body modification. Removable as well. You would need to decide on what bags that you want to use whether from another Triumph(Sprint, Tiger, etc) or Givi or other brand and see what the mounting brackets look like. You would need to custom fabricate and design the system to work. Unless you can contact those who have done it or know someone good at custom fabrication, you're on your own I'd say. Many have mounted bags on bikes that weren't designed for them, but it always involves custom design and fabrication. Maybe you can search YouTube for inspiration.
I have that color T595 that you posted. Looks like a very good install; nice and clean and looks factory.