The lineOfAction is a bit smarter than just connecting to excitation. You can do things like firing based on the velocity of the change in curve length for instance.
You can tell the fiber to be more or less sensitive to these changes through lineOfAction.
To add extra volume, beyond just preserving it, is currently not supported. Not ideal, but possible is to shot sculpt the muscle bake after it’s done.
Artificially changing the rest shape (effectively art directed shapes) has been discussed at Ziva internally. I believe the plan is to support this in the future but not sure which release that would be.