I don't think the word exchange is appropriate here. Goblin Welder had to be retemplated, after all. What about "Put the top two cards of your library into your graveyard, then put up to two cards from your graveyard on top of your library in any order"?

Goblin Welder was retemplated not because exchange was not workable, but to make it absolutely crystal clear what happens if the artifact on the battlefield is destroyed ("As the new wording makes clear, both targets must still be legal as the ability resolves in order for it to do anything."). I suspect it also clarifies that an artifact creature sent to the graveyard this way dies. In any case, the new wording is not even a functional change.

They still use "exchange" with the same rule baggage on new cards: Shrewd Negotiation, and even used it for library and graveyard before (Morality Shift).