I'm putting this here for future people because we've been beating our heads against this for a few days, and the solution is not intuitive at all.
Background: We had a Service order that needed to not require a diagnosis. In Administration, where you can create new orders, we added <Default> to Insurance-specific Information and unchecked "Diagnosis required". We found that a diagnosis WAS required at all locations except one. We were even able to toggle the dx requirement on and off within the actual document by clicking the green pencil and changing the doc location.
Solution: I created the order when I was logged into our system at a specific location rather than the parent location. This auto-assigned that default insurance to that specific LOCID.
I want to spread this information to all possible corners, as even our vendor didn't know what the issue was. What's incredibly frustrating is there is no indication on the order that there is a location assigned, and we haven't been able to find documentation of this in Centricity's help documentation.