How to add code to dll?

[jonwil]

I have a Windows x86 .dll file (specifically its a mixed mode Managed C++ and Native C++ dll if that makes a difference) and I want to add some new code and data
to that dll including adding the necessary entries to the .reloc segment. What's the best way to do that?

The code and data I want to add is already in a different version of the same .dll as binary assembler instructions (obviously I would need to fix up the addresses to point to the right places in the dll I am modifying) and I don't need to touch the managed side of things.