but how can I make sure, that the discount will only be applied to NEW orders within that special offer period?
I MUST enable recurring orders, otherwise no domain fee will be affected by that discount (because domain fees are recurring orders). But if recurring payments are enabled, every recurring invoice, that is generated between start and end date, will get that discount, even if it is the second, third, etc. year, don't they?
These discounts should only be available for new orders, in other words: for the first year.