Is there any way to migrate from desktop edition to workstation ?

Hi,

I have an old installed base of desktop edition machines ( running on vmware for hardware independance ), using this software:
subscription-manager list
+-------------------------------------------+
Installed Product Status
+-------------------------------------------+
Product Name: Red Hat Enterprise Linux Desktop
Product ID: 68
Version: 6.6
Arch: x86_64
Status: Not Subscribed
Status Details: Not supported by a valid subscription.
Starts:
Ends:

Recently I 'upgraded' my licenses to workstation licenses wanting to be able to use more CPU and RAM for a bit higher workloads.
Imagine my surprise when I now no longer am able to patch the machines since I have the wrong kind of licenses.
Complete reinstall is not really a good way to go as a change in opreating system may force us to certify our own products again.

In case I do have a reinstall, what would be the easiest way to do that, given that I want to have a mirror image of the existing desktop machine, but with workstation packages ?

Regards,
Tommy