Existing AR Invoices to separate GL Account

Our Controller has an interesting request.

We have a year’s worth of invoices sitting in our A/R account to “internal” customers (Part of the same company). HQ Accounting would like these moved to a separate “Intracompany A/R” GL Account. We’ve got it set up so that future invoices go to the new GL account, but I’m trying to figure out the best way to get the existing ones moved. There are over 15K invoices, so doing anything one at a time is out.

I have some ideas. Not being an accountant (or even close), I don’t know if this first one is verboten or somehow terrible practice. And for the second one, I don’t know how to pull it off in Epicor.

Idea 1:
GL Entry debiting Intracompany AR, Crediting Cash. Then create a Cash Receipts transaction, and apply it to the Invoices in question. End result is the balance of the invoices is transferred to the desired account. Issue: Manual entry crediting cash sounds dubious.

Idea 2:
Create a Credit Memo (negative Invoice) for this customer, but somehow mess with the GL Control so that it debits the Intracompany AR account instead of <whatever CMs normally debit from>. Apply the negative balance to the existing invoices. Issue: Is this a thing, or am I dreaming?

We change account structure once and needed to update all of the open invoices to a new account. Epicor support had a fix for this issue.
I had to supply a list of all of the invoices with the new account number.

We actually came up with what I think is an elegant solution. I’ll let you know Monday when we’ve run it by the higher level accounting team.

We created a new “bank account” linked to the intracompany AR account, and can attach cash receipts (that don’t credit cash, but the internal AR account) that is applied to the invoices. It works as intended in our Test DB. We have a meeting Monday to see if it is all good from the accounting POV.