It has been a few years but I just got annoyed with the regenerating every time it saves and searched for "Civil 3D regenerates on save" and found this thread
A few questions:
1. Version of Civil 3D?
2. Have you installed all the service packs
3. Have you used fields to label your assemblies?
What is "fields to label your assemblies"
I am not sure if I have done this or not?