I always allow avast to update itself whenever a new version is available…In the 2 or 3 years I’ve been using Avast 4 [not sure exactly how long it’s been], it hasn’t noticeably changed in how intrusive it is. The same applies for the latest update. It is acting perfectly fine on both my computers, and is respecting how I have it set up.
In other words: update. Nothing will change for you on the surface.