...And (in addition to Sam Harwell) You can use constants and can change any particular <PropertyGroup/>
(only "release" for example) this way:
<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
<Optimize>true</Optimize>
.....
<OutputPath>\your_projects\bin\$(SolutionName)\$(MSBuildProjectName)\$(Configuration)\</OutputPath>
<IntermediateOutputPath>\your_projects\obj\$(SolutionName)\$(MSBuildProjectName)\$(Configuration)\</IntermediateOutputPath>
<DefineConstants>TRACE</DefineConstants>
</PropertyGroup>