Assigning software with multiple enterprise licences

In typical fashion I appear to have created a new complication to resolve with the asset management section.

We have enterprise licences for much of the core OS and server products, so have created the appropriate enterprise licences to assign the detected software to.
However I have discovered a number of servers and workstations that aren't using the enterprise license key so I want to assign these rogue installs to either another enterprise licence calling it something like OEM version, or to individual licences.
However it seems that once an enterprise licence is assigned there is no choice for which licence to assign a workstation to.

Any suggestions as to how I get this resolved please, short of re-installing the OS on the offending workstations and servers!

Regards,
Andy