Error updating order data

Hi,

We are using OSM 7.2.2.2.2, In one of our tasks, we need to update the order data. For achieving that we are using this approach

xmlns="http://www.metasolv.com/OMS/OrderDataUpdate/2002/10/25">

<Add path="/MobileServiceData/MobileServiceDetails/ServiceLineItem/ItemReference/SpecificationGroup"> <Specification>

<ActionCode>ADD</ActionCode>   

  <Name>IMSI</Name>

                        <DataTypeCode>Text</DataTypeCode>

  <Value>{$IMSI}</Value>

  <PriorValue>{$iccid}</PriorValue>

     </Specification>

</Add>

Till now,only one service line item is available in this task data so we are able to achieve the desired result . But due to some change in requirements, now we are receiving two service line items in this task data may the number can increase in future.