I tried this with very limited success. As near as I could determine, you just open the AHII mission .mis file with the new editor, make some change and then save it and create a new .res file. One in air spawn mission seemed to convert, the rest crashed when I tried to run them. This was back in the late beta days by the way and for a while all the missions that had ground takeoff were crashing on spawn. I have not tried it lately.
