<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<ItemGroup>
<MySourceItems Include="file1.resx;file3.resx">
<MyAddMetadata>true</MyAddMetadata>
</MySourceItems>
<MySourceItems Include="file2.resx">
<MyAddMetadata>false</MyAddMetadata>
</MySourceItems>
</ItemGroup>
<PropertyGroup>
<MyValue>Hello</MyValue>
</PropertyGroup>
<Target Name="NewItems">
<CreateItem
Include="@(MySourceItems)"
Condition="'%(MyAddMetadata)'=='true'"
AdditionalMetadata="MyMetadata=$(MyValue)">
<Output
TaskParameter="Include"
ItemName="MySourceItemsWithMetadata"/>
</CreateItem>
</Target>
</Project>