Almost every project I write has a configuration file and its content varies from one environment to another.
In this case, managing multiple configuration files can make life a lot easier.
There are different approaches for doing this, I'll link to a demonstration made by Scott Hanselman a while back - Click Here.
In short:
1 - Create configuration builds.
2 - Add a batch file at the root of the project as written below.
3 - Add a Pre-Build action to execute it.
The batch file 'copyifnewer.bat' content:
@echo off
echo Comparing two files: %1 with %2
if not exist %1 goto File1NotFound
if not exist %2 goto File2NotFound
fc %1 %2
if %ERRORLEVEL%==0 GOTO NoCopy
echo Files are not the same. Copying %1 over %2
copy %1 %2 /y & goto END
:NoCopy
echo Files are the same. Did nothing
goto END
:File1NotFound
echo %1 not found.
goto END
:File2NotFound
copy %1 %2 /y
goto END
:END
echo Done.
The pre-build action to be inserted:
"$(ProjectDir)copyifnewer.bat" "$(ProjectDir)web.config.$(ConfigurationName)" "$(ProjectDir)web.config"