Everyone seems to discover a different subset of functionality so some of these may be obvious to you.
Importing PRG’s is easier than I realised. When creating a new module and associating it with a PRG you can actually specify multiple PRG’s to create multiple modules.
VOPP creates a PRG file when building a DLL using the Single app build and System builder. You can use this PRG file instead of the AEF created for the DLL for your imports. If you do this then whenever you change your DLL you will just need to touch the module linked to the PRG to get the changes. No more deleting the application and reimporting the AEF.