I took over GM'ing in the middle of the campaign. At the start of Sins of the Saviors. The only thing I have changed so far is the fight at Rimeskull. As written I thought it was pretty bad since the boss just shows up pre-buffed WITH SPELLS THEY DON'T EVEN KNOW. I changed it so he actually confronted the party first. I mean he has been slumbering for the past 400 years or so. He gets waken up and the first thing he does is cast very specific spells and then immediately fly out and attack.
I had him fly down and confront the party first. He has 16 int and knows common. I pictured him as being somewhat curious about what was happening. It is not like he had anything to be afraid of. I was also trying to give the party some non-combat ways of resolving the fight if they wanted to go that route.
I have also added a nameless cult dedicated to Karzoug that is has been causing the party some grief and giving them bouts of paranoia. A gnome sapper alchemist was at Rimeskull boobytraping the Runelord heads. It was going pretty good for him until he got exploded by Arkryst.