We had to do the same thing here. To top that sequel was quite a task. Mike had a couple of good conceptual humour and character ideas, which got me back into it. ↗
Don may yawn at the idea, which he often does, but the great thing about Don, he has confidence in me and Mike and Ed and Leslie and Steve, that we're not going go out and do stories that will put people to sleep. ↗
In the year and a half I was on SNL, I never saw anybody ad lib anything. For a very good reason - the director cut according to the script. So, if you ad libbed, you'd be off mike and off camera. ↗