Under mild conditions (room temperature, no forcing conditions or strong catalysts), which direct conversions by nucleophilic acyl substitution are feasible?

Acyl transfer is favourable only from a derivative with a better leaving group to a nucleophile giving a derivative with a poorer leaving group. Acid chloride to ester (A) and anhydride to amide (C) fit. Ester plus chloride to acid chloride (B) would expel the poorer leaving group ethoxide. Amide plus neutral ethanol (D) would expel $\mathrm{NH}{}_2{}^{-}$ and is not feasible at room temperature.