Sure, the DM can tweak anything -- I do it all the time, and very seldom run a "stock" module, personally. The point is, why write it that way in the first place? Give players some options. Most dungeon crawls give the players exactly that -- they can open the door to the west, take the corridor to the east, or go down the stairs. They can fight or negotiate with the monsters. The choices are up to them. The dungeon structure puts limits on what they can do to keep things manageable for the DM, but a well-designed dungeon crawl has an inherent amount of free will built in -- take a look at, oh, Keep on the Borderlands, for example. There's a basic structure, but player choices give the adventure form. I'm saying that a strictly linear structure is inherently weak.
My gripe about this particular adventure is that it takes away player free will by preordaining a set of events, with set outcomes. Sure, the DM can interject, modify, etc -- but modification, IMHO, shouldn't be required in order to give your players options.
I'll get off my soapbox now.