Business Layer Framework

I started to know about some business layer Framework (for .NET framework) last month. And the last month (until now) I learn about Mere Mortal Framework there is so many things that before I always confuse about how to make a 3-tier programming more fast, and the answer is the framework like this. With this framework we can save a lot of 3-tier stuff that we must do, but until now I still don't have an idea how to make it reverse (as you know this framework has a wizard that make it easy to create business layer step by step), I mean I can change the code in business layer later after the code generation by the wizard. The "change" here is a lot of change, for example adding new field or adding a new table with some rules and business logic.