Deal wide discount GET/UPDATE not available

I can access the discount per product line, but I cannot get any information about a deal wide discount.
Is there a way to get/update the “additional discount” through the API?

For example in my order I have 1 item with a 20% discount and then I need to apply a 10% order wide discount.

I cannot simply change in my case from 20% to 30% for the line, because the final value would be wrong, in this particular case the formula would be 1 - (((12.5 * 600) * (1 - 0.2)) * (1 - 0.1)) / (12.5 * 600)) = 0.28, so in this case to “fake apply” a 10% discount to a 20% discount I’d need to change it to 28% but I don’t want that anyway as I lose context information.

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