@Mandea:
Hm, works fine for me. When it says "Your download is starting", it should start downloading... make sure your pop-ups are not disabled and take a look at your browser settings.
@Fatt_Shade:
Maybe I'll work on the battle cry, but later. BTW it takes about 3 files to implement a new talent for a unit.
To add Champions in Knight's set go to special_params.txt and under sp_lead_warrior, amongst other units add Champions.
I'm not sure what exactly you mean by changing something in older savegames, but I'm pretty sure it's impossible. Each campaign/session has it's own set of savegames and, in my opinion, mixing them would be more difficult than making new King's Bounty game.
To change what skills must be learned before being able to learn a certain skill (ex: Voice of the Dragon) go to skills.txt, then go to the skill you want to edit and under deps=[...] delete the skill you don't want as a requirement (ex: the skill that doesn't even exist in your picture).
I had the problem where it says 0 damage, but actually kills the whole stack... It happened when I tried to edit Red Sands. I think it's somewhere in arena.txt or arena.lua , but I'm far from sure since it may actually be in any txt/lua file or maybe even somewhere else.
I can't help you with the dragon/spellbook problem, but there is a chance that it's somewhere in arena.lua. And if these problems get fixed after starting new game then I'm not sure if it can be helped.
Good luck.