Once a PO is created, the accounts associated with the item at that point are assigned to the PO. You have several options.
1. Use SQL to change the account indexes in the PO header and line records (NOT recommended unless you know exactly what you are doing)
2. Close/Cancel existing POs and enter new ones. (Not a pleasant thought if you have lots of them)
3. Allow the postings to move forward as is and re-class the amounts through journal entries. This is the easiest plan unless some POs will be open for months or years.
You might consider a hybrid of 2 & 3, closing and recreating any long term POs and working through the short term ones.
BTW, this also occurs with Sales Orders!!
Another thing to consider...when you rolled down the account number changes, no GL entries were created. This means that all the debits to the old Inventory Asset accounts are still sitting in the old account number. However, Credits for new sales will be taken from the new account. Journal entries are needed to reconcile these differences as well.
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