replace headlamp coded pieces?

[fisheses]

I just bought a used headlamp assembly off Ebay and it looks like it comes with all the parts that mine currently has, and the part numbers on the decal are the same. How will I know if there is some kind of coding that needs to be done or are there electronic parts that I should just reuse from my old assembly and put in the "new" assembly anyway, like the ballast that I can see on the outside of the casing? Are there pieces/parts on the inside of the casing that I should also reuse? Thank you, folks!