new parameter for a concurrent progam. How to know the variable name?

I need to add a new parameter into "Invoice Print Selected Invoices" CP. currently this CP has number of parameter include Transaction number low, transaction number high. Both transaction_number_low and transaction_number_high are using the same value set called AR_RAXINV_TRX_NUMBER with range set to low or high. The new parameter, that I want to add, let call it "PARA 1". PARA 1 has value set called para_1_value_set ( 1 character in size only ). My user requirement is when user enter 'Y' into PARA 1 parameter, it will pop up message if the the transaction number low <> transaction number high. if transaction number low = transaction number high , no pop up message.