I normally only soak my reeds in water, before I play.Gerhard, do you soak your reeds in anything?
I agree that the most obvious answer to the green is from the oxide reaction with copper in the brass, but there are some nickel compounds that are also green. If you mouthpiece is down to the nickel plate, clean and dry most of the time, then you add a wet solution that reacts with the nickel, there is some possibility of a different chemical reaction.
Thanks,Lacquer on a table strikes me a a bad idea...both chemically and in terms of creating an uneven surface. Chemically that being close to your mouthpiece is much more likey an issue than brass in your mouth. Yes its bare brass but none of the alarmists around here have presented anything that resembles data to suggest that there is any health threat.
To me you are going into darker territory to fix what is likely a non problem.
My suggest is that if it bothers you this much do the job right and have it replated. Personally, Id just play it.