Convert Login from Windows Authentication to SQL Server authentication? I have an account that is setup for Windows authentication. The account is used by SSRS for running reports and has various permissions in multiple databases. I need to convert this account to use SQL Server authentication.

I don't see a way to change it in SSMS. Is there a way to "flip a switch" and make it use SQL Server authentication?

For details as to why I want do this, see this question.
I think your best bet would be to script out the server level permissions granted to the Windows Login and save the SID, delete the Windows Login and recreate it as a SQL Login with the same SID, and finally grant the permissions back on the Login. 

This way the login will have it's server level permissions recreated and retains it's database level permissions since the login will match the database user via SID. 

    CREATE LOGIN [LoginName] WITH PASSWORD=N'PASSWORD'
            ,DEFAULT_DATABASE=[master]
            ,CHECK_EXPIRATION=OFF
            ,CHECK_POLICY=OFF
            ,SID=[SID]