Maybe, guess we have to see. But having the whole Dominion turn "renegade" kinda ruins the Odo hero arc. Or maybe it's just a couple normal changlings.Plus, the episode is called Dominion.
I think the Picard DNA is a Red Hearing....after all they could get it from the Picard Bio bot body.
The most obvious thing...the most unique thing....is Locutus. Picard is just about the only borg to keep their memories, be part of the collective and be a singular named individual.
And taking control of all the linked ships on Frontier Day seems to be obvious. As soon as they said "all the ships are networked" I heard "for easy take over". Plus it is exactly Agnus did in season 2....
Other stuff seems silly....like "use Picards body to call the Nexus to destroy the Sol system and all of Starfleet? Have a Changeling copy Picard....and...and...and....um, tell the Federation to surrender? Could Changeling Picard activate the Federation Starfleet Self Destruct?