[Edi]

You can add stuff to a map with RanDom, but it cannot actually modify the poptypes. It just adds extra defenders.

Unless Ballbarian has found some way to hack the game to allow poptype editing.

One must always keep in mind the differences of what you can do with mod tools and what you can do with map tools. This is one of the places where confusion can happen.

In this case you would need to both mod the barbarian king and then add it to a map via RanDom. Such a map would be unplayable without the mod.