Commerce Server Blog

Through code, we can create discounts. For more information check below site.
http://msdn.microsoft.com/en-us/library/aa544659.aspx

The problem with this approach is that the discount will be created but it is in non-approved stage. So, when you use newly added discount code as it is now approved. The approach is to call “ActivateCampaignItem” method after creating discount.

For more information about this method refer to
http://msdn.microsoft.com/en-us/library/microsoft.commerceserver.marketing.webservice.marketingwebservice.activatecampaignitem.aspx