We introduced an interactive extension mechanism, which allows us to extend programs and systems verified with Coq. In the mechanism, only adding new constructors into existing inductive types are allowed, but adding parameters into functions or constructors are not.
In this paper, we introduce a novel mechanism, which allows us to add new fields into record types. We also show the limitations of the mechanism arising from the type system of Coq. The method used in the mechanism is also applicable for adding parameters to existing constructors and functions. We explain problems occurring when we apply the method into them.