nolcoz: It depends on what you want to do. You could take the mod (the progs.dat and models) and use it straight up. Just make more maps for it.
Or if you want to fold those changes into another mod, the author does provide QuakeC source code that you could study, on his website: http://www.ajaysquakesite.co.uk/raptors.htm
Depends on how much of a QuakeC ninja you are (or want to become).
Althoooough actually (glancing at the QuakeC right now) it does look like a moderately simple/localized change. I think he replaced the fiend model, modified some of its animation frame sequence in the QuakeC, and edited a fiend-related text message or two. Hard to tell for sure though since nothing marks the changes.