Change SQL Server settings without restarting services I can change SQL Server settings using Management Studio or programmatically as described e.g. here.

I would like to make this changes WITHOUT the need to restart SQL Server services. Is there any trick to do so??
It depends on what settings you changed based on http://msdn.microsoft.com/en-GB/library/ms189631.aspx. Some require a restart (RR), other can be done via RECONFIGURE

There is no trick or workaround. At all.

Edit, now we know it is Authentication mode...

This is automatically deals with the instance name

 EXEC xp_instance_regwrite 
    N'HKEY_LOCAL_MACHINE', 
    N'Software\Microsoft\MSSQLServer\MSSQLServer', 
    N'LoginMode', 
    REG_DWORD, 
    1; -- or 2 for mixed


Restart is still needed