I can attest that this is the true way to activate Ada with Camilla's dress.
I turned on swap Ada with Camilla, than turned on swap Clair with Ada (Wanted to play the main game as Camilla), and viola! Its now Ada in this dress. For default Clair skin.
Still don't know how to play the game as Camilla lol.
There is a trainer to make you ada, but its the trenchcoat one, you could save models with that, but since its not ada with the red dress I dont know. The creator either needs to make it for all adas or make a clear swap to claire.