The term belay is often used to cancel an order in military settings. The definition indicates it just means to cancel. However, would asking a superior (in a civilian private sector employment situation) add an improper tone to the request?
Belay is commonly used in nautical settings (not military) to mean "stop." Any sailor might use it in this context; it is not limited to belaying orders.
Using it in a different setting might come across as endearing, pert, obnoxious, or charming, depending on your relationship with the superior with whom you are speaking, and the manner in which you use it.
However, the word belay in and of itself is not rude or offensive.