We give a discount only if the customer has picked a self-delivery. Can this be done?

You can set the conditions under which the discount will apply. To do this, in the pricing component, open the Constraints tab.

Set all the values of the fields and price options for which you want to give a discount. In our case, we will set the Self-delivery checkbox.

To cancel the selection of the value, click the (-) icon to the right of the field value.

See the example in action: