Hudson - The Boeing manuals can be particularly vague in certain areas! This is not the way the Boeing pilots and engineers would have it but the way of the Product Liability lawyers. In 1983 the product liability premium for Boeing was USD$50,000,000 and for UTC, (which includes Pratt & Whitney), $250,000,000 so you can imagine how much it would be to-day!
I think that if I heard a big bang I might consider not using reverse on the engine with the fire but if it was just a fire warning then I think I would use it to speed up coming to a halt.