Yes, I have when I converted to H4 but you will need to use an LED rear lamp otherwise it will dim substantially when you brake. The light output is much improved and if you use an Osram Nightbreaker you will get even more light output.
I then opted for one of the Jockey's Boxenstop clear glass and modern reflector headlamps which also use H4 lamps and found that their 35watt lamp was as good as the 60/55 one in mine. I'm not sure if the Boxeys unit will take the heat from a 60/55 lamp as it's all plastic but in my case I decided to fit an HID unit, here's a link to my thread on the Scooterotica site
http://scooterotica.org/forum/viewtopic.php?f=7&t=33894Colin