On clean installed SQL Server 2008 instance if you change the Table you may see this message:
This dialog states: "Saving changes is not permitted. The changes you have made require the following tables to be dropped and re-created. You have either made changes to a table that can't be re-created or enabled the option Prevent saving changes that require the table to be re-created."
This can be fixed by changing settings for SQL Server Management Studio.
Open: Tools > Options
Do uncheck "Prevent saving changes that require table re-creation".
Once you do that save will work.
I think Microsoft should made it unchecked by default.