A RewriteLink is a kind of ScopeLink, that provides many functions useful for implementing term rewriting. It is not typically used by itself; rather, it serves as a base class for many link types, most importantly the PrenexLink.
The methods that it provides are not accessible via atomese, nor in python or scheme, nor are they intended to be; rather, the C++ class provides a low-level store-house of useful methods for performing different kinds of analysis of terms, and the re-writing thereof. As the warning label says: "Caution: Do not open. Risk of electrical shock. No user serviceable parts inside."