Hi, I try and think that one time that you choose one VOICE you can't erase it, you only can change it for another one

I would to know one thing in account at this question, if I select a style, go to MODE 2/2, in the empty fields A, B, C, D, I select a VOICE,(I think that is for the right hand 'cause I go to VOICE and can select one voice), but my question is, I left this screen and play with this style, but when I change the arranger to A, B, C, D, the right hand don't change, what's wrong?. Thanks