Using the OpsMgr command shell (PowerShell) you can quickly export a management pack to XML for importing later on.
Here’s the format for the command-shell, as simple as it needs to be:
Export-SCOManagementPack -Path “C:\myDirectory”
There are other parameters that you can use for the command line. See all those here: Export-SCOMManagementPack
Incidentally, the import works for both OpsMgr and Service Manager.