Do you have any sources for this change? Cause from domestic media, what I could tell is that both the shortened version and the stretched version still will use the same wing and fuselage design with the only change being 6 less cabin modules for shortened version and 11 more cabin modules for stretched along with an extra central fuel tank to keep range at 3000nmi.Now with stretch version they will add CFM wings and add new material like composite in main body and aerodynamics will change as well.
COMAC has done the full-scale box section test and verification of the T800-level composite wing of C919 back in 2021