ZDoom

Is it possible to make a patch using just mapinfo/zscript etc. to change map orders and map exits in Hexen Deathkings so it continues the journey after defeating Korax in Hexen?

It's certainly possible; I would imagine something like Wadsmoosh could be modified to perform such a merge. The problem, as with most other things, is that nobody has yet actually done such a thing yet. Perhaps you could be the first?

Actually, there's this.