I have done some investigation in to this issue and thought I would pass on some of my findings and successes. I have successful activated a bootcamp partition and a vm with hard drive connect to the bootcamp although activating one causes the other be become deactivated. When switching bootcamp and bootcamp VM (or vice versa)the OS first comes up deactivated but within a couple of minutes becomes activated. I have also found that if internet access is required for this to happen.
I have switched between both 5 times successfully. So far this seems to be workable. I also have made some progress as to what a windows activation is actually tied to. I have found that after an update from win7/win8.1 to window 10 the activation is tied to the physical machine. I believe Microsoft is using the bios GUID and manufacture information as part of the machine identifier. which can be seen in windows by the command "wmic csproduct" in windows. This GUID is set by the manufacture and is unique for for each machine.
I have tested this by replacing the hard drive in a machine and loading windows 10 skipping both requests for a activation key. Within minutes of restart of a completed installation the machine came up activated (requires internet access). Another discovery I have made is that each VM you create gets a unique GUID. It is in the config.pvs file in the vm,s bundle as the "VmUuid", "SourceVmUuid" xml tags. To change it you may edit this file when the vm is not running and deleted from parallels (save source when deleting) and open with parallels after editing. I have found you need to also edit the config.pvs.backup file to match. I have tested that Microsoft is using this by changing this GUID in a activated vm and after changing the machine came up deactivated and would not activate. Based on my tests and findings I don't believe a single instance of windows 10 can be activated on more then one machine at a time with out saving off info for each activation and restoring with each unique machine. But once Microsoft has a record of the initial activation of a machine and its GUID activation seems to occur automatically as long as internet access is available.
With this Knowledge this is how i setup my current configuration.
1. Create a Bootcamp partition and install of Win7/Win8.1 and upgrade to Win10. Once this is activated microsoft should have a record of your physical hardware and it unique GUID.
2. Create a Parallels VM and install of Win7/Win8.1 and upgrade to Win10. Once this is activated microsoft should have a record of this vm and it unique GUID.
3. Shutdown the vm you created in step 2.
4. Open configuration for the vm created in step 2 and go to the hardware tab and delete the hard drive(you may want to keep a copy of this vm before doing this). Now use the + to add a new hard drive. Select bootcamp as the type then select the bootcamp partition. click ok configure the desired mem etc... and start the vm.
Since the this VM and its GUID are all ready registered with Microsoft It should activate automatically.
I do not know if there any limitation on the number of activation for each unique machine. I suspected there is but i think it resets after a period of time. Perhaps this is why some people have experienced a need to wait 24 to 48 hours for activation to occur. The only test for this is to use it. I personally don't change back and forth that often and I believe this will work for me.
I believe the only differences that Microsoft can detect in a parallels VM is the GUID as the hardware is the same for all vm created. This would mean that you could create a new vm and set it,s GUID to one that has been registered and get automatic activation but I have not tested this. I also do not know the implications of having more then one vm with the same GUID. I would suspect that parallels might uses then uniquely identify the VM's.
Hope this helps let me know if you have any questions
Last edited: Aug 24, 2015