Most of us with smaller motorcycles have the same problem as I have, we all have an old motorcycle or scooter which we use for riding around our neighborhood. The value and age of the motorcycle let you think twice about buying a new exhaust pipe, but rust on your exhaust pipe is in full swing and probably sooner than later your exhaust pipe is corroded beyond repair.
You did think about spray painting the pipes, but the spray paint at the local Do-It-Yourself store is not able to resist heat over 200 degree Celsius and after a week or two you back to where you started with the spray paint being burned off the exhaust pipe. The solution is provided by a company in Thailand which manufacturers high-temperature resistant spray paint, the spay paint comes in 4 color shades being Mat-Black, Glossy-Black, Mat-Silver, and Metallic Silver. The high-temperature resistant spray paint can endure temperatures as high as 650 degree Celsius, what is about the melting point of your magnesium wheels.
The manufacturer markets the spray paint for jet-engines and high-temperature exhaust systems, and it will not flake or peel off when exposed to high temperature. The spray paint is available in spray cans of 400cc. You can contact the manufacturer, to ask about the nearest sales location, by calling 02-3180133