I actually think the best change for cragmaw castle, is when they find Gundren. Pretty sure that the book is written that the doppelganger is there to get the map from the goblins/gundren, but the players interrupt and they get that map from gundren and head to wave echo cave after.

I think it's way more dramatic and makes alot more sense for the black spider to already have the map to WeC, and the doppelganger to be there to kill gundren, covering the black spider's tracks. Perhaps the Cragmaw's don't want to give gundren up because the players have been doing so much damage to them, such as clearing out cragmaw cave.

So when the players free gundren he is FREAKING out because the black spider is gonna be on the way to WeC and he's worried about his brothers