That would require modding some of the game file(s), which can't be done yet I'm afraid. Modders are waiting for one of three things to happen currently I believe:
1) The rest of the Forge Tools are released
2) The regular text versions of the Gameinfo folder files are released
3) A tool to convert the binary versions of the Gameinfo folder files back into text files are released.
Both options two and three have been requested as an interim method to get modding started, as the rest of the Forge Tool suite isn't ready yet for whatever reason. However, we're all still waiting until something happens.