(I gotten asked this so many times :-) , I figured I would expand my original answer.)
So as an example, in Debug mode, I want to include a Setting.bundle that consists of Root.plist and a submenu Extra.plist.
In Release mode, I want to include a totally different Root.plist and no Extra.plist in the app's Setting.bundle
My .csproj file is going to look like this:
<ItemGroup Condition="'$(Configuration)'!='Debug'">
<BundleResource Include="Settings.bundle\Root.plist" >
</BundleResource>
</ItemGroup>
<ItemGroup Condition="'$(Configuration)'=='Debug'">
<BundleResource Include="Settings.debug\Extra.plist" >
<Link>Settings.bundle\Extra.plist</Link>
</BundleResource>
<BundleResource Include="Settings.debug\Root.plist" >
<Link>Settings.bundle\Root.plist</Link>
</BundleResource>
</ItemGroup>
Note:
As shown below, in Debug Xamarin is including additional menu items into my Root.plist and in Release they are not. Also my Additional Settings submenu is no longer available and now are labeled with XXXX Release
Debug mode result:


Release mode result:
