customer alternate payer in payment receive

Dear All,

I am asking on Customer alternate payer.

1 May I know for Customer if the payer (different from customer) defined in SD partner function, can we get the payer field updated in FD document, document type RV after billing created?

2 For vendor alternate payee, we can reallocate to alternate payee during F110.

should we do reallocate for customer?

If yes, where can do reallocate? F-28 or Fb05 cannot.

If no, then what is the purpose of alternate payer in customer? if head office only can meet this requirement, then what is the purpose of alternate payer in customer master?

Thanks