How can I change the seeded search flag to NO in the event phase for INV: Batch Processing for Inter

I have two Price lists for Intercompany Transactions. I do not want pricing to select the price list based on the precedence. I am assigning the individual price list to the transaction type and customer site and shipping network. So I would like to change the seeded search flag to NO for the pricing event INV: Batch Processing for Intercompany Transfer Pricing so that it does not automatically choose the price list based on the precedence but look at the pricelist assigned at customer site and transacaiton type. But the check box is greyed out. How can I enable it