Modding

Noob question from me.
I understand how to create a new hero, but how do I add a newly created hero to the selection window when creating maps?
Is this written into the map file itself? 
I.e., do I need to edit all the original maps in order to add one new hero to the selection window? Or is there an easier way?

There are 2 options here: either write the hero into the map itself, but then he will only be available within that specific map, or write him into MapObjects\_(AdvMapSharedGroup)\Heroes\Any.xdb, and then he will be available on other maps as well.

There is one caveat though, and it lies in maps where certain heroes are banned. The point is that in such maps, a list of available heroes is compiled and it is contained in the map itself in the map.xdb file. Naturally, there's no way for a new hero to appear in that list, so on such maps you'll have to add the new hero manually.  

This is roughly what it looks like in map.xdb.

<AvailableHeroes>
        <Item href="/MapObjects/Dwarves/Egil.(AdvMapHeroShared).xdb#xpointer(/AdvMapHeroShared)"/>
        <Item href="/MapObjects/Dungeon/Eruina.(AdvMapHeroShared).xdb#xpointer(/AdvMapHeroShared)"/>
        <Item href="/MapObjects/Haven/Nathaniel.(AdvMapHeroShared).xdb#xpointer(/AdvMapHeroShared)"/>
        <Item href="/MapObjects/Stronghold/Hero6.(AdvMapHeroShared).xdb#xpointer(/AdvMapHeroShared)"/>
        <Item href="/MapObjects/Dwarves/Ottar.(AdvMapHeroShared).xdb#xpointer(/AdvMapHeroShared)"/>
        <Item href="/MapObjects/Academy/Havez.(AdvMapHeroShared).xdb#xpointer(/AdvMapHeroShared)"/>
        <Item href="/MapObjects/Stronghold/Hero7.(AdvMapHeroShared).xdb#xpointer(/AdvMapHeroShared)"/>
</AvailableHeroes>