There are two options:
1. Use the account generator workflow - PO Requisition Account Generator - defined in the file poxwfrag.wft with
the ITEM_TYPE = POWFRQAG to default the accounts for requisitions.
2. Use POR_CUSTOM_PKG (PORCUSTB.pls) procedures to change the charge account as desired.
Details of the usage of por_custom_pkg is in the iProcurement Implementation Manual