epidiatassomai describes adding something to an established covenant in Galatians 3:15.

The sole attested use concerns adding something to a covenant already made, within a comparison about what no one does to a human covenant.

1. Add to an established covenant · dominant

   In Galatians 3:15, the present middle indicative form occurs in the comparison concerning a covenant made by a human; the APB renders the clause, “just as no one rejects or adds to a covenant made by a human.”

   Galatians 3:15

In the Anselm Project Bible: In Galatians 3:15, the APB presents the relevant action with “adds to” in its covenant comparison. This rendering confirms the clause's overall sense rather than isolating every feature of the Greek form.