I always try to play it safe and replace used copper sealing rings. Copper is soft and malleable which is why copper sealing rings will sometimes reseal, but you run the risk of having one or more of the rings crack and leak from becoming thin and brittle from re-use.
You can, BUT!!! If you smell gas from your engine bay, you will need to replace them immeadiately. Leaking gas is not something you want in your car!
My personal opinion is that the copper washers are cheap and pulling the fuel rail isn't simple on the MkII because of the air chamber and throttle body (not to mention the vacuum lines). Given the amount of time it would take you to get back in there, I would just replace the washers.