  We perform an off-shell treatment of asymptotically decelerating spatially
flat FRW spacetimes at future null infinity. We obtain supertranslation and
superrotation-like asymptotic diffeomorphisms which are consistent with the
global symmetries of FRW and we compute how the asymptotic data is transformed
under them. Further, we study in detail the effect of these diffeomorphisms on
some simple backgrounds including unperturbed FRW and Sultana-Dyer black hole.
In particular, we investigate how these transformations act on several
cosmologically perturbed backgrounds.
