Operations Manager 2007 comes with several standard management pack templates. You can use these templates to create a new management pack and then customize that management pack to your requirements. This approach provides an alternative to creating a new management pack to store the overrides for a sealed management pack.
One of the available MP templates is the OLE DB Data Source Template. Use the connection string properties to specify the instance to which you want to connect. You can find more information on how to construct OLE DB connection strings, on MSDN Connection String Syntax.