As a native English speaker, I would say that yes, you may use them interchangeably. When I think of using them in my head, there's really no difference whatsoever. To me, they are the exact same meaning. However, while they are interchangeable, I would say "goof off" is more common. I am more likely to say "goof off" than "goof around". Instead of "goof around" it sounds better to me to say "fool around". "Fool around" in the context of doing something silly or stupid is very similar to "goof off/around". "Goof" is more silly or stupid and "fool" is more annoying and obnoxious or irritating. However, it has another meaning (sexual). So "goof off" and "goof around" are the same and it sounds best to use "goof off" or "fool around". Of course different regions and individuals may use words slightly differently, but this is my opinion.

The phrases are indeed very similar. However, in my experience the contextual usage can be slightly (very slightly) different: - "goof off" might have a stronger meaning of shirking one's responsibilities, while - "goof around" is, as mentioned previously by Gertie, more similar to "fooling around" without the sexual connotation, more like "doing silly things for the fun of it". At least based on the instances where I've seen these phrases used. Hope this helps :).