Reverse engineering the original client and writing your own game server application, pretty much. If you know all the packet data structures the client expects from the server, you'll be about halfway there
Anyway, don't bother trying to contribute/volunteer as a developer though if you don't have years of mmorpg development experience
When a game is completed it is compiled and the game cannot be modified unless they left certain parts intentionally open sourced. You cannot modify their data unless you knew how to decrypt the data. From what I've seen this game is programmed from an object oriented language like C#. I don't need "years of MMORPG Development experience" since the genre is only a few years old itself. I make games. I was just interested in seeing how people accessed the game files that I thought were stored Server Side. You see, MMOs have two versions of the game. Client Side, Server Side. Thus, reproducing an MMO or "reverse engineering" it would take files straight from that studio.