So how hard would it be to transplant Blades in the Dark characters, faction game, etc into a Alt-History Lovecraftian London?
So long as we acknowledge the existence of the supernatural and steampunk technology the game should run with just a bit of spackle. Reconfigure the gangs and change the fringe cults to historical societies like The Golden Dawn or Freemasons; that should do it.
Or am I missing the forest for the trees? Any and all advice is appreciated.
As long as you come up with new factions and make sure all the Actions, special abilities and inventory items still make sense with the new setting, you should be fine
You might want to look at The Kerberos Club for details on the era, and some ideas for how to crank up the oddities if needs must. Victoria can be a pretty solid replacement for Scurlock, if she’s presented right. Alternatively, A Study in Emerald is great fodder for an, ah, elder ruler.
What Thomas Berton​ said. You’d need to reskin factions at the very least.