Hi.
Is this per Item or per Transaction? Some Items can be blocked to be discounted for example, also You can play around with the Lower / Upper bound properties of the Item...
If You want to block the transaction to be tendered when a discount is applied, bigger then something You have defined outside RMS let say, then it must be a personalized development. It's not hard to do, but You need to define more things.
Hope this helps, talk to Your RMS Partner.
BR, A.