Is there a way to edit maps for this game? Or make them larger?
Is there any way to modify the game to create yopur own scenario?

To your first question: not directly, as far as I know. But the Insecticide patch/mod includes an option for a huge single land mass, a la Pangaea.

To your second question, again not directly. But you can edit an existing map using hex editors (the hex codes you need are a google away) or a program like MomEdit 1.3. So while you can't build or move preexisting cities, or surround your starting city with adamantium and quorx, you can assign them a different race; or change which wizards you'll be facing; or even throw your own wizard some extra gold and/or mana, to give yourself an unfair advan— I mean, a head start.