Possible to apply an Office Professional Plus 2013 key to Office 365 Business Install (or quick conversion to allow key usage)

I have a client, with Business Premium licensing which currently has Office 365 ProPlus installed on a number of PCs. It has recently come to light that they have a volume license key for Office Professional Plus 2013 and so would like to use this instead to lower their 365 licensing down to Business Essentials.

Is there a way i can apply the Office Professional Plus 2013 key to the Office 365 ProPlus or is there a way i can alter the Office installation to allow this?
The client is reasonably large and spread over a large winding building so any suggestion to avoid having to visit PCs individually would be really helpful.

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Vasil Michev (MVP)Commented:
No, those are different SKUs and you will have to download/deploy the corresponding version of Office in order to be able to activate it with the VL key.
David Johnson, CD, MVPRetiredCommented:
Is there a way i can apply the Office Professional Plus 2013 key to the Office 365 ProPlus or is there a way i can alter the Office installation to allow this?

No, they are different versions.  If you had office 2016 proplus then yes you could and perhaps with downgrade rights (if you have SA) use it for office 2013. In your situation you have to uninstall Office 365 and install office 2013
support01Author Commented:
Thank you both Vasil and David. You're right, it would seem that uninstallation and reinstallation will be the way forward which i am testing right now.

To soften the blow, i'd at least like to attempt to transfer the Outlook profile from O365Business to OProPlus2013 to avoid setting up the profile manually.

Since the profile was not showing in Controlpanel/Mail due to the different versions (16.0 vs 15.0) I've exported the registry keys from:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Profiles\Outlook, renamed to 15.0 and imported.
I can now see the profile in Controlpanel/Mail.

I've entered "686c9881-008b-49f5-83ab-ef158c37c421@domain.com" into the server name (also tried outlook.office365.com).
I've manually edited the connection details to include 'Anonymouse Auth' and 'Connect over HTTP' etc. but I am still getting issues connecting Outlook "The Connection to Microsoft Exchange is Unavailable".

From another questions on SpiceWorks, it would seem that what i'm trying might be possible, however, they don't give detail on how they achieved this in full.

If anyone could offer suggestions on what i might try, that would be really helpful. I'm keen to avoid bothering users for their Outlook credentials in order to configure Outlook from scratch if possible.

David Johnson, CD, MVPRetiredCommented:
From my experience you can upgrade from lower version to higher version but not the reverse.7

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support01Author Commented:
Thanks both, looks like this will be manual work after all.
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