Is it permissible to write 70 grams of gold in the marriage قائمة (dowry list), knowing that only 30 grams were agreed upon, and that custom dictates the preparation of this قائمة to complete the marriage?

The dowry is a right for the woman according to Islamic law. There is no objection to it being gold, money, or furniture, whether paid in advance, deferred, or partly so, depending on the agreement. If part of the dowry is deferred gold, there is no objection to that. It is customary in some countries to list in an inventory what is purchased with the spouses' money for furniture as part of the woman's dowry, which she takes upon divorce. It is permissible to list items in the inventory that are not physically present, thus making them a debt and a deferred dowry. If the furniture is made part of the dowry, it is the wife's property, and the husband is not obliged to compensate for any damage to it. She has the right to reclaim it upon divorce. This custom is permissible as long as it does not contradict Islamic law.