You can add as many XML structure CustomInfo elements as necessary to any Part or Assembly element.
The following CustomInfo example element contains three values:
<CustomInfo Origin="AssemblyXML" CreatedBy="ERP">
<CustomInfo Value="8899" Info="ERP_ProductionBatchID" />
<CustomInfo Value="000345447" Info="ERP_ProdOrderID" />
<CustomInfo Value="A456771122" Info="ERP_Material_No" />
</CustomInfo>