Admin can set discount rules based on Shipping Method.
For making this discount rule select Discount Rules tab.
Now choose Shipping Rule
Now you can choose Add New Rule.
Fill Rule, Restrictions and Validity tabs accordingly.
After saving the rule it can be seen in the given table below.
Now you have to give permission to your rule to give discount on the product you have chosen.
Click on the Setting Tab.
Check Shipping Rule as shown below.
After checking these rules, Choose among First Match Rule, Best Match Rule or All Match Rule and click on save rule button below.
Now your Rules are active and if anyone choose the shipping method which you have chosen to give discount the discount is automatically applied.
The Discount can be seen on the cart page in cart totals.
Now whenever you want to disable this discount rule, you don’t have to delete it, just go to Setting Tab and uncheck this rule.