Ok time to close this thread cause to runs in circles with half the people saying it can't, half saying it can, an no one actually testing what they recommend to see if it actually works
Dont get me wrong I don't mean any offense and help is always welcome, but what if it was your PC that has an issue, and half the people you ask say yes, half say no, and no one is there to actually guide you through the steps.
Can it be done?
So long story short. It normally can NOT be activated, but also it kinda CAN be activated but it's not worth the time. The eval versions can not be activated as the expiration period is actually hardcoded but... never say never with software.
What needs to be done in order to be activated, is to install a full enterprise version over the eval version. To do that you need to change the type of windows as Jerry said from EnterpriseEval to Enterprise by going to
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion Why you need to do that, cause windows check to see if there is an eval string, and if they find it they won't perform an upgrade.
After that, Download a newer and full Enterprise ISO and perform an
upgrade (not a clean install). Doing so will replace the non-upgradable files of the eval version with the ones from a full version, and thus keeping whatever is installed. Run an activation script and you will have a full Ent. Version.
And no, there isn't any other way that I know of, and no Medicines or script will manage to do it as the windows activation services of an eval ISO are different than those of normal ISOs and that is why you get errors with any Medicines.
Is it with it doing it?
In my opinion no. Anything can go wrong and if someone is going to use an ISO to refresh their current build might as well do a clean install and be sure that nothing is wrong. If something does go wrong since we don't know details about the current installation, one will end up spending more time and multiple restarts, and end up doing a clean install anyway, so save that time and perform a clean install. Additionally, we need to remember that only clean ISOs can be used to do the in-place upgrade and not the custom Ent. versions we have here as I doubt they can perform an upgrade.
Conclusion:
So up to the OP if he wants to spend several hours trying to do what I described above and hopefully it will work, or download one of the awesome custom Enterprise versions we have here, make a fresh install and end up with a much better and probably faster PC.
This thread tho will close as a lot of suggestions were given and I don't see anything else that can be added but if there is a need for a follow-up, contact a mod/admin to reopen.