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gugie had successfully brazed a steer tube into a chromed fork crown using A LOT OF FLUX. I don't know if the crown was triple plated or not.
You may be able to do the same with silver solder and Nickel, being very careful with the temperature.
HOWEVER, you have a non-structural part. There are some excellent adhesives that you can use. Talk to a good vintage auto detail shop. I don't remember the brand, but the window felt adhesive I got a while ago was really good.
And, then you have the advantage of being able to paint your frame first, then simply glue the badge on. No need for careful masking.