Thanks for the quick response 
You can expect MAAS to setup the IPMI credentials during commissioning
Awesome! - Does this include pulling the IPMI IP too or does that still need to be set manually in MAAS?
If the machines are still able to reach out to MAAS and you have enabled hardware sync during deployment, MAAS will also reflect the new network config you apply to the machine
Most of my concern here is around decommissioning customer servers after use, I’m not too bothered about changes customers make while it’s in their hands. The isolated VLANs will still have a DHCP server with PXE pointing at MAAS, so I’m wondering if it’ll still be just fine starting the decommissioning process while the machine is on a different network to the one it was initially discovered on.