When you need to seal a Management Pack there is an excellent guide from Jonathan Almquist: http://blogs.technet.com/b/jonathanalmquist/archive/2008/08/19/seal-a-management-pack.aspx
However, if you have installed CU4 or later MPSeal might fail with the following error:
Could not load ManagementPack [ID=Microsoft.SystemCenter.Library, Keytoken=31bf3856ad364e35, Version=6.1.7221.61]. ManagementPack not found in the store.
Cannot find MP File “Microsoft.SystemCenter.Library.mp” in any of the search directories.
That is because Microsoft.SystemCenter.Library.mp has not been updated to the new version number. Either you can edit your MP and change the version number or download an updated version from Microsoft:
Do not not import this MP to your SCOM installation just add them to your repository for MPSeal.