hi fado,
Your question is a bit unclear to me and so I can't answer it.
If this is your first arranger keyboard, then I would suggest that you forget about registrations for now and concentrate on styles only. Styles are the core of arranger keyboard and so it's crucial to understand how styles work and what capabilities they have.
Registration is not accompaniment: registration is just a snapshot of current keyboard state (keyboard settings), which we can later quickly recall (by pressing one of 1-8 buttons). And because registration contain all relevant keyboard settings, it can also override some style settings (without changing style itself).
But without really understanding "how it works", it can be confusing when we wish to modify something to our liking.
I really recommend to study Reference Manual and try things on your keyboard. And if there's specific question, you're welcome to ask.
Bogdan