At some point in your career working with SQL Server, you will run into a situation where the wrong edition of SQL Server has been installed on a server and will need to change the edition for licensing reasons.  Whether it is Enterprise Edition where Standard Edition should have been installed, Enterprise Edition where Developer Edition should have been used, or my favorite, Evaluation Edition where the 180 day trial has expired and Enterprise Edition isn’t going to be used, the only route available for downgrading the edition is to uninstall and reinstall SQL Server entirely.  SQL Server Setup makes upgrading editions a piece of cake with SKUUPGRADE as a command line option for going from Standard/Developer/Evaluation to Enterprise, but anything else requires a full uninstall and reinstall to change the SKU/Edition and then restore all of the system and user databases to the new instance, which typically means a lot of work.  I hate having to restore system databases and avoid having to do it if possible, so here is how I do this process and minimize the work required:

No matter what you are going to have to do an uninstall and reinstall of the SQL Server instance to downgrade the SKU.  However, you can save yourself some time and the headache of trying to restore the system databases if you are careful about what you do.  I have done a plenty of SKU downgrades in the past and the easiest way to do it, and I am not saying this is the Microsoft supported way but that it works if done correctly, is to:

  1. Take a good backup of all of your databases (system and user).  
  2. Run SELECT @@VERSION and note the specific build number of SQL Server that you are currently on.
  3. Shut down your existing instance of SQL Server.  
  4. Copy the master, model, and msdb database files (both mdf and ldf), don’t move them copy them, from the current location to a new folder that you mark as readonly. 
  5. Uninstall SQL Server from the system.
  6. Reboot the server.
  7. Install SQL Server Standard Edition.
  8. Apply the necessary Service Pack and/or Cumulative Updates to bring the instance up to your previous build number.
  9. Shutdown SQL Server.
  10. Copy the master, model, and msdb database files (both mdf and ldf) from the folder you saved them in to the correct location for the new install and remove the readonly flag from the files, and change the file ACL’s so that the SQL Service account has Full Control over the files.
  11. Startup SQL Server and if you did it correctly it will startup and be exactly where you were before you made any changes, with all of your user databases online and you should be ready to let applications connect and resume operations.

If you screw something up in the above, you still have your backups and you can run setup to rebuild the system databases and then go about following the Microsoft supported path for restoring the system databases and then user databases into the system to bring it online.  Essentially the file copy is no different that what would occur through attach/detach you are just doing it with system databases which is not explicitly supported, but it does work.  The key is to have your backups from before you do anything so you have the supported route available if you encounter an issue.  The only issue I have ever had doing this set of steps is that I didn’t set the file ACL’s correctly and the database engine threw Access Denied errors and failed to start until I fixed the ACL’s correctly.  This can save you many hours of frustration and downtime trying to restore everything since the database files are already there and it is just some small copy operations to put them where you need them to be.