Hi Wolfgang,
My work involves woodworking.
One thing for sure, to re-stain, you definitely need to strip off any coating that's already on the surface of the wood, sand it down to get rid of any old stain residue that may be caught in the wood grain. If your your furniture has intricate carvings or profiles, you will need a high level of expertise so I suggest you send it to a professional. Unfortunately there are not many good carpenters left in S'pore who can do a good stain/lacquer job so please expect difficulty to find one and of course, a high price for the work done.
I know this because my work is mostly done in places like Vietnam, China & Philippines. Nobody wants to be a carpenter here anymore.
Call me tomorrow and I'll try to answer any other queries that you may have.
melvin 91540064