By default, SQL Server Management Studio (SSMS) will not let you save changes to the designs of your tables. When you attempt to do so, it wants you to drop and re-create the table. You will typically see a dialog similar to the following:
However, SSMS will actually let you perform such a change without have to drop the table and re-create it. To enable this feature, you need to select Tools / Options from the Menu. Then, navigate to Designers / Table and Database Designers and uncheck the option to “Prevent saving changes that require table re-creation”.
Now click the OK button and try saving your table design changes. Voila!
I owe a big thanks to my friend Jack for teaching me this trick. It has saved me a lot of grief!