Some Modding Questions
 

1. Is it possible to mod 0-gem items? That is, itens that does not cost any gems to forge? How?

2. How do i make the Dwarven Hammer unique?

3. Is there any way to mod all items forging costs as a whole, instead of one by one? I wish to reduce all magic items forging costs (to balance the Dwarven Hammer becoming unique)...

Re: Some Modding Questions
 

1 - I don't think so, since cost is determined by primary path level to forge, and the minimum value is 1.

2 - Set its construction level to 8. Note that this will mean that you are also requiring greater construction research to obtain, and it will have a nation modifying effect similar to the Hammer of the Forge Lord.

3 - Aside from making the "Forge of the Ancients" global cheaper? Not AFAIK. You could reduce the research costs globally, but it wouldn't be restricted to construction...If you're talking about a particular nation, you could give it a magic site with a forging bonus as a start site (but note that the bonus would be available to any who captured the capital) or give the nation units with forge bonuses.