Gary,
Welcome to the BurgmanUSA forum! I am more familiar with the 650 version, but there are folks here that have done modifications to their 400's also. Two performance items I am aware of are the Malossi variator which can add some responsiveness to the transmission, and the Leo Vince exhaust. Aftermarket windscreens are available from Givi and Gustafsson Plastics. I believe Givi also makes a rack mount for the 400 so that you can add a tail trunk. Corbin is in the process of designing a seat for the 400 also. So there are definitely some aftermarket goodies out there that can help you taylor your 400 to your own preferences -and I'm sure there will be more to come.