I had two 200' lengths of chain that needed to be regalvanized and had 50' at one end that was pitted, so removed. Had a welder cut a good link open, remove the galvanize around the weld, add the other chain, and TIG weld it. Then the weld was dressed so it matched the other links and the whole chain was regalvanized.
If you have your chain joined by welding, it must be done by a professional welder with a TIG machine to ensure no impurities in the weld. While intellectually I know this is now the weakest link in the chain (G4 3/8"), with a 5, 400 lbs working limit and 16, 200 lbs tensile strength, I'm sure something else is going to let go before that link parts.
Ted