`Fold` `ReplaceAll` using `rules` sorted by a custom ordering function:

    order[a_Rule, b_Rule] := (a /. b) =!= a;

    expr = A^3 B^4/b + A^3 B^4 C X/d;
    rules = {A^3 B^4 -> Γ, X -> ρ, A^3 B^4 C -> Δ};

    Sort[rules, order]
>    {A^3 B^4 C -> Δ, X -> ρ, A^3 B^4 -> Γ}

    expr /. rules
>    Γ/b + (C X Γ)/d

    expr /. Sort[rules, order]
>    Γ/b + (X Δ)/d

    Fold[# /. #2 &, expr, Sort[rules, order]]
>    Γ/b + (Δ ρ)/d