Restrict changes in External Services of Operation in Work Order

Hi,

I am trying to restrict the changes ( Addition/deletion/changes ) in the External service requested for a operation in Workorder.

I tried with Exit IWO10009 but I am not able to compare the  run time value with old value of the services.

I used  BAPI_ALM_ORDER_GET_DETAIL to get the old entries of External Services. But how can I get the run time value.

If we change any thing in the operation ( including External Services ) system should throw an error. Please help.