Well you can look into how DFHack for Dwarf Fortress was redone. It involved a C++ decompiler written in clisp. Since then Ghidra was released, so the process

Well you can look into how DFHack for Dwarf Fortress was redone. It involved a C++ decompiler written in clisp. Since then Ghidra was released, so the process is somewhat simpler, if not as much *fun*.