Is there a way to prevent setting the same property more than once when deserializing a object?

Question

Deserializing the following yaml fragment using YamlDotNet:

       bill-to:  &id001
            street: |-
                    123 Tornado Alley
                    Suite 16
            city:   East Westville
            city:   West Westville
            state:  KS

Will call the city property setter twice, once for each value..

Is there a way in YamlDotNet to prevent this sort of behavior and make YamlDotNext explode when the same setter is called the second time?

I'm using YamlDotNet in this case, and YAML in general, as a configuration format for my application, and it is very counter-intuitive for users to be able to assign to configuration keys different values...