Change Windows Server Edition without Re-install

The below steps are tested on Windows Server 2016 core, but should work in Windows 2012 as well.

C:\>dism /Online /Get-CurrentEdition

Deployment Image Servicing and Management tool
Version: 10.0.14393.0

Image Version: 10.0.14393.0

Current edition is:

Current Edition : ServerStandardEvalCor

The operation completed successfully.

C:\>dism /Online /Get-TargetEditions

Deployment Image Servicing and Management tool
Version: 10.0.14393.0

Image Version: 10.0.14393.0

Editions that can be upgraded to:

Target Edition : ServerStandardCor
Target Edition : ServerDatacenterCor

The operation completed successfully.

C:\>dism /Online /Set-Edition:ServerStandardCor /AcceptEula /ProductKey:WC2BQ-8NRM3-FDDYY-2BFGV-KHKQY

Deployment Image Servicing and Management tool
Version: 10.0.14393.0

Image Version: 10.0.14393.0

Starting to update components...
Starting to install product key...
Finished installing product key.

Removing package Microsoft-Windows-ServerStandardEvalCorEdition~31bf3856ad364e35~amd64~~10.0.14393.0
[=====                      10.0%                          ]
[==========================100.0%==========================]
Finished updating components.

Starting to apply edition-specific settings...
Restart Windows to complete this operation.
Do you want to restart the computer now? (Y/N)
 
Press Y to restart the computer.


References:
Technet Key for Windows Server 2016:  https://technet.microsoft.com/en-us/library/jj612867(v=ws.11).aspx
Technet, Use DISM to convert Evaluation to Retail version, https://technet.microsoft.com/en-us/library/jj574204.aspx
Windows IT Pro Center: DISM Windows Edition-Servicing Command-Line Options, https://technet.microsoft.com/en-us/library/hh825157.aspx