First off, you'll have to rename the physical default.aspx and default.aspx.cs to something else, say "newDefault.aspx and newDefault.aspx.cs". Then, open those files and change it with the ff:
from newDefault.aspx:
Code:
<%@ Page Language="c#" Inherits="AspDotNetStorefront._newDefault" CodeFile="newDefault.aspx.cs" %>
from newDefault.aspx.cs:
Code:
public partial class _newDefault : SkinBase
Second, you'll have to do a global search from Visual Studio to change every default.aspx in AspDotNetStorefront solution.
In your InetMgr (IIS), select the website, right click to select "properties", navigate to "Documents" tab, and add "newDefault.aspx" on top of the other existing documents.
I haven't actually try this, so let us know if this works.
*Make sure to have a full backup of it first before making these changes.