Well the way I look at t is this: a blower forces more air into the engine. With more air you need more fuel. In the AA kit it includes a new fuel rail and injectors. How is the car going to know to pump more fuel into the car if the DME isn't remapped? Unless the computer knows that their is a blower and it needs to compensate with additional fuel the car will run lean. That's why AA says you have to mail your DME to them for remapping.
The link to the Bentley Manual is posted in the E36 section. It's a sticky so it is at the top of the page. It's a large file, about 97mb do it may take a few mins to download.