Manually edit your .csproj files to include the correct files depending on build configuration.
Android:
<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
<AndroidManifest>Properties\AndroidManifestDebug.xml</AndroidManifest>
</PropertyGroup>
<ItemGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
<None Include="Properties\AndroidManifestDebug.xml" />
</ItemGroup>
<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
<AndroidManifest>Properties\AndroidManifestRelease.xml</AndroidManifest>
</PropertyGroup>
<ItemGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
<None Include="Properties\AndroidManifestRelease.xml" />
</ItemGroup>
iOS:
<ItemGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|iPhone' ">
<None Include="DebugInfo.plist" />
</ItemGroup>
<ItemGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|iPhone' ">
<None Include="ReleaseInfo.plist" />
</ItemGroup>