It is not uncommon that a config spec can contain 50 lines or more and making a call for each line sounds to be not very user friendly and makes the DSL script quite chatty. Especially when the config spec is passed as a parameter from a parameterized build it is in my opinion easier that one can pass multiline parameters in a single call. 
Therefore I would like to suggest to keep the possibility to pass multiline values but to also allow configSpec to be called multiple times. I think this covers all view points and use cases then.
Same goes for loadRules and mkviewOptionalParameter.

How does this sound?