Answer: ONLY, when ONE of TWO things occur
Standard of Practice 3-2.
Any change in compensation offered for cooperative services must be communicated to the other REALTOR prior to the time the REALTOR submits an offer to purchase.
After a REALTOR has submitted an offer to purchase, the listing broker may not attempt to modify the offered compensation with respect to that cooperative transaction.
Standard of Practice 3-3
3-2 above does not preclude the listing broker and cooperating broker from entering into an agreement to change cooperating compensation.