Replacing the tracks in the resource files is quite straight-forward.
Extracting them is as easy as opening the resource file in a hex editor and deleting everything in front of "MThd".
To replace the track, copy a new midi track to that position and edit the resource size accordingly - that would be the 4 bytes before "MThd".
I made a small tool that does exactly that. It expects either a midi file or a HnH resource file with a single midi track as a parameter and will generate another file with the same name (i.e. ronald.res becomes ronald.mid and vice versa). Alternatively, you can provide the desired output filename as the second parameter.
In Windows, you can simply drag a file onto the program icon to do the conversion.
Binaries for Windows/Linux (47 KB)
Source code (it uses non-standard classes and functions, however it should be more or less self-explaining)