This one is pretty simple. An aircraft substitution is all it takes to lose 4 F seats. AS will likely downgrade in reverse order of UG. Thus, the certs. may well go if there aren't any takers. The question is what is AS offering beyond the obvious which is required by DOT and its own COC, e.g., the fare difference between F & Y. In OP's case, that would be the return of the GGU's. If it's simply, an ask with no customer service gesture associated with it, why on earth would you take this? If you are worried about the DG, perhaps reroute?