Dear Oliver,
as I see from the answer (since my Spanish is much worser thant Tilmans) thyt your concern is about the changes during the project. Originally ASAP is waterfall-based as the methodology for ERP implementation. So you have in theory accepted BBP and you should follow it. Bu us usuall as Tilman wrote beside probably core ERP nobody is able to write down 100% perfect the desigh.
On the other side you have now Agile ASAP that enables changes and incremental implementing.
Indeed ASAP is methodology to implement SAP systems but rather limited in the area of project management itself. If you need support for change management - how to handle them properly with minimizing risk for the project you schould take any of project management methodology like PRINCE2 or PMI for example.
The worst thing you can have on project are creeping changes that seamless will become uncontrolled and you will be in troubles. Now agility is buzzword so you can not prevent changes as they are immanent part of the business. Changes are good but you have controll them.
Regards
Waldek
