You will have to provide a context for such a word.

overfix can be used as a verb. It is related to the popular verb fix and not commonly used. Only dictionary dot com mentions the word if you search diligently online. Also, if one uses the words over and fix separate, it can mean something else.. Based on what I find, overfix means fix (with a higher degree). Also, usually we write over-fix (watch the hyphen between the two words over and fix).