Theory on how York intends to become a Celestial Dragon:
She can't just think they'll let her become one. And she can't have thought the way to go about it was to force the government to come and kill them all. The only reason would be that she needs to force a Gorosei to show up in person. Why? To do a personality swap with Saturn. She may have access to Law's lineage factor via the Seraphim program and where has she been working out of? The old devil fruit laboratory. Doffy set up this possibility, but maybe York will be the one to actually try it.
Even if an artifical Ope-Ope no mi isn't involved (it would be hax), Atlas did mention that she could change her appearance to whatever she liked, so York could probably do the same.