You already have a full permission, right?
Then forget about the outline permission, it's been superceded by the full grant of permission.
Regardless of what you do, you have a full grant of permission for a house on that site.
Using the permitted design, amend/alter/extend it to suit your requirements and lodge the alterations as an amendment to the approved development.
If permission is granted, great.
If refused, you still have the original permission. And you can also appeal the decision to An Bord Pleanala.
If they permit, great.
If they refuse, you still have the original permission.