Some changes in SQL Server require that the table in question be dropped and recreated behind the scenes. It’s possible that this might cause a problem for some users, so it seems that in the SQL Server 2008 Management Studio, Microsoft has disabled this by default.
You will receive the message:
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.
Anyway, to allow these changes to occur, go to Tools –> Options, and under Designers, uncheck “Prevent saving changes that require table re-creation”. That’s it!