CX? Customer I guess. Generally they won't do a discount to add MLB, but may give you another discount if your account is qualified for one. Example, you may get $10 off for 6 months, it would be off your base package, even if they are giving it to you in addition to adding MLB.
Free MLB is new customer signup only, ultimate or higher.
People who had MLB and are calling to cancel are often offered discounts to keep it, but not always. The least likely to get a discount is an existing customer adding the MLB service for the first time.