By adding some CSS, you can customize the text for each rule.
Each method is surrounded by the following CSS tags
proshipment proshipment-method-[shipment method id] proshipment-rule-[rule number selected]
proshipment proshipment-method-16 proshipment-rule-10
16 is the shipment method id and 10 is the rule selected
You can easily add some CSS specific to a rule as shown in the following example where we have highligted the Spend More text