there is a great tool now ready for the public, whit this tool you can make easy customizations to the MP.
The System Center Management Pack Authoring Console 2007 has been released to the Web! If you’ll be at the Microsoft Management Summit next week, stop by the the Authoring Session SO04 – Tools and Best Practices for Authoring Management Packs for Operations Manager 2007 session for additional information.
System Center Authoring Console (Release Candidate)
This powerful console enables you to author Management Packs offline and get them developed quicker for the Operations Manager 2007 SP1 platform.