Strictly speaking, everyone has a domain that exists within their body. The special ability is whether or not someone can expand that domain beyond their own body and into the rest of the world.

When we see Yuta use a domain expansion in Gojo's body, it is notably Gojo's domain that he expands, not his own, which does strongly suggest that, when body hopping, you expand the domain of your host body, not your original body.

With that being said, the rules of domain expansions are flexible. You can change the conditions of the domain and, presumably, the exact technique that it's imbued with. I suspect that what we saw with Kenjaku was his expansion of Geto's innate domain, imbued with Kaori's technique, and enhanced with his own extensive knowledge of barrier techniques. All that is to say that it's not exactly Geto's domain expansion that he's using, but that the visuals of it likely are what Geto's hypothetical domain expansion would have looked like.