Hello all - I have the standard ## cert user (example: •##MS_PolicyEventProcessingLogin##) sql installs during instantiation and wanted to know what the ramifications of changing the [type] of the generic users?
So essentially any server principals (logins) that start with the ## are created by the system during installation and should not be touched or dropped. I can look specifically into each account to determine exactly what they are used for but I think for your question you can run into a lot of issues if you start playing with these accounts.
Should any of these accounts need to be restored I believe that a restore from your master database backup would be required, if you haven't got that (but of course you have) then you need to either rebuild the master database or reinstall SQL Server. Just remember that a rebuild/reinstall will lose all your logins and other security information amongst other losses as well.