Mapping tables in Entity Framework

Question

I performed the following task at the below link provided which worked fine for me using Entity Framework 5.0 with Visual Studio 2010.

http://blogs.msdn.com/b/simonince/archive/2009/03/23/mapping-two-tables-to-one-entity-in-the-entity-framework.aspx

However, if the database schema needs to be refreshed, how do you prevent the changes you made to the designer from getting lost and doing them all over again?

This is not going to be pretty for a database that has lots of tables....