If v is an interpretation, it maps (all) terms to elements of corresponding universe, while possible actions are only some formulas, . . .

Maybe we're not using the terminology in exactly the same way.

For me, an interpretation of a theory is an ordered pair (D, v), where D is a set (the domain of discourse), and v is a map (the valuation map) satisfying certain conditions. In particular, D is the codomain of v restricted to the constant symbols, so v actually contains everything needed to recover the interpretation. For this reason, I sometimes abuse notation and call v itself the interpretation.

The valuation map v

• maps constant symbols to elements of D,

• maps n-ary function symbols to maps from D^n to D,

• maps n-ary predicate symbols to subsets of D^n,

• maps sentences of the theory into {T, F}, in a way that satisfies some recursive rules coming from the rules of inference.

Now, in the post, you write

Each such statements defines a possible world Y resulting from a possible action X. X and Y can be thought of as constants, just like A and O, or as formulas that define these constants, so that the moral arguments take the form [X(A) => Y(O)].

(Emphasis added.) I've been working with the bolded option, which I understand to be saying that A and 1 are constant symbols. Hence, given an interpretation (D, v), v(A) and v(1) are elements of D, so we can ask whether they are the same elements.