Yes. Open the customer under Customers, and (when the Marketing Hub module is on and Allow Refer a Friend is Yes) you will find Cashback % plus Digital Amount to Referring Customer and Digital Amount to Referred Customer fields. Enter a value to override the site-wide setting for that customer only; enter -1 to fall back to the default (the label shows the current default). The override is used when that customer places orders (cashback) or when their referrals complete a first purchase.