SAP by itself will create the TO with the quantity mentioned in the delivery. If your users create TOs with a higher quantity, then they change it manually. Have you asked them why they are doing it.
I mean they must have a reason. Once you understand the reason, you can educate them or may need to adjust your design and customizing.
I remember cases where the customer service people did not know how much quantity is in a drum or in a bag, so they just entered the quantity as it was in the order by the customer. Nobody will open a 25 bag to remove 2 kg just because the CSR had booked 23kg.
If warehouse people pick 25, then they are actually right. Just restricting them cannot be the first choice. First you need to find the reason why they are changing the quantity.