Will taking percocet recreationally on rare occasions be harmful?

Yes harmful: This is exactly how addiction begins.

Recreational drug: Recreational use of prescription drugs is the most common drug abuse in USA. Any opiate drug if used recreationally can lead to addiction and becomes a habit. It is best to avoid such drugs as they are also illegal if not prescribed for you and provide no benefit. They can also show up on any drug testing if needed for job etc.