I've done this in Panorama without using Expedition, by loading partial configs from one DG to another by loading a partial configuration from the source device group in the running-config as per https://live.paloaltonetworks.com/t5/Configuration-Articles/How-to-move-or-copy-objects-in-configuration-from-one-location/ta-p/71904
You need to start with the dependencies i.e. tags, addresses, address groups, apps, app groups, profiles, profile groups etc. then you can copy the policy. You can copy all pre- or post- rules at once by using the pre-rules or post-rules Xpath.
I found an old tech note for PAN-OS 6 quite helpful for this process https://live.paloaltonetworks.com/t5/Tech-Note-Articles/Panorama-Device-Migration/ta-p/62527 even though the device migration process is largely automated today.
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