I'm not sure I'd want to modify other people's bikes. Opening an independent service shop I could see- Fluid changes, tires, maybe replacement of stock parts like bearings and brakes. Modifying or installing aftermarket parts carries a load of possible problems with it. There are all kinds of aftermarket parts, and a lot of them are not street-legal. What happens if you damage the electrical system of a brand new GS while installing some cheap aftermarket hand warmers? What happens if you install some new luggage on a motorcycle, and the owner goes down after 50 miles, totals his bike, and tells his insurance company that your "improperly installed" aftermarket luggage threw off the balance of his bike, causing him to "lay 'er down?"
I am BY NO MEANS trying to discourage you from following your dreams! Just make sure you're ready, and that you consider the potential pitfalls as well as the potential success.
Chuck Norris can blow bubbles with beef jerky.
Chuck Norrris has never gotten a Jeopardy question wrong. Jesus has missed two.