Change internal function of a package [duplicate]

Answer 1

Try

?assignInNamespace

to replace .HMR.fit1 in the HMR package with your version.

Possible duplicate of :

How do I override a non-visible function in the package namespace?

Answer 2

For a quick testing you can use the trace function with edit=TRUE to modify the function, this will do the replacing in the proper namespace and also allow you to use untrace to revert the function back to the original. These changes will not last beyond the current session.