It's impossible to find him. You can change the specialization using scripts. You can do it for a specific map, or you can do it using game scripts. For example, you can take script #67, which gives each hero of the Conflux a new specialization (snipers, wizards, nomads, etc.). You can also edit them according to your own wishes.
As I understand it, this script only works when the Neutral town is selected. In addition, script #39 edits the advanced abilities of heroes, supplementing them. There you can assign a specialization to any monster, but you cannot change the specialization based on skills and magic.
For example, it would be nice to give Adelaide the Cold Ring specialization, like the elementalists - with double damage. Or give Adrian the Fire Magic specialization with increased power of fire spells by 25%:smile04:.