When you create overrides for a Management Pack in Operations Manager 2007, it's a good idea to put them into a custom Management Pack instead of the Default Management Pack:
For example, if you use the Exchange Management Pack, create an "Exchange Overrides" Management Pack and store all your Exchange overrides in that Management Pack. You'll probably want one of these override Management Packs for each Management Pack you use (assuming you plan to apply overrides to it, of course).
If you don't store your override in an override Management Pack, the override automatically goes into the Default Management Pack. This won't cause problems during day-to-day operations, but makes it difficult to remove the Management Pack later. In particular, it creates a dependency between your Management Pack and the Default Management Pack that is not removed even when you remove the overrides:
I talk more about how to remove this dependency in this post.
Jonobie Ford posted a great article on the Best Practice for Creating Overrides in Ops Mgr 2007. Check
If you created overrides before you knew about storing overrides in your own Management Pack and need
Pete Zerger (of System Center Forum ) sent us a checklist at firstname.lastname@example.org to use while importing