No. You cannot make partial payments or short pay invoices in the UPS Billing Centre. In order to make a payment in the UPS Billing Centre, you must pay the full Amount Due.
If you dispute a Delivery Service Invoice (Domestic/Export), any credits relating to your dispute will be applied to a future invoice, so the Amount Due on the invoice being disputed will not change.
If you dispute an International Services Invoice (Import), any credits relating to your dispute will be applied to the current invoice. Once the credit is applied, the Amount Due will be adjusted.