Is it permissible for there to be an increase of $200 per kilogram in the process of exchanging crafted gold for raw 24-karat gold, under the pretext that it is a fee for raising the karat, and is this increase permissible only in the case of exchange?

The transaction mentioned in the question is impermissible because it involves exchanging gold for gold with an increase. The Prophet (peace be upon him) said: "Gold for gold, and silver for silver...like for like. Whoever gives more or asks for more has engaged in usury; the one who gives and the one who takes are equal in this." (Narrated by Al-Bukhari). It is not permissible to give the worker the weight of his worked gold or silver, and then give him an additional payment as wages for his labor.