There should be no problem soldering with the plating on. Remember
that a standard sterling object becomes, in essence, plated every
time that you solder and pickle it. Electroplating fine silver will
not change the way the piece behaves. You may wish to grind through
the plating a little in the specific area that needs soldering.
Note that this is not the case with rhodium plating which will most
definitely bubble and discolor. That’s another beastie entirely.
Just be sure of what the plating is.
Perhaps I’ve missed something, but this has been my experience.
Take care, Andy