Try whatever you like, if it was 'bespoke' it wouldn't be called SAP, it would be called 'jeff's shiîty in-house developed software'.
Can you customise SAP with additional components? Indeed you can, most of these would be off the shelf packages, unless you are a government department who enjoys haemorrhaging money and missing deadlines.
Let's see if I can help you to understand. Microsoft (and others) now have a set of offerings labeled 'platform as a service' (PaaS) which rely on the assumption that their SOFTWARE will meet your individual needs. By your reckoning, they should shutter these offerings, as 'if it ain't bespoke, it won't do'
I'll remember that next time I'm chatting to a CEO about building a predictable, scalable IT function.