How to add Drupal Coupon discount for selected category or item only?
You you can do it by adding new RULES. If you are using Percentage Coupon then you must have a rule in the list of rules list named "Calculate coupon with percentage amount".

Clone this rule &amp; add more conditions according to your need like "Order contains products of particular product types" or "Order contains a particular product".

Its totally upto you to use conditional based discount and disable the default coupon redeem rules.