RE: Void sales invoice to the correct GL account
The point of Leslie's post is that if you had used the PSTL solution then all the account idexes attached to OPEN / WORK and HISTORICAL transactions would have been modified to the NEW account numbers.
All the Account numbers exist only in the GL tables, after that the Account number that is stored with the transaction in (as example) sales is an Index. This index is a short numeric value that is easy to spot i the table, and much smaller for purpose of storage in the table.
Anyway the point is that we are trying to get at is that by simply creating new accounts and making them the NEW transaction default, it does nothing to address all the HISTORY transaction that still reference the OLD account index.
Long and short is that you will not be able to simplify the process and if you VOID and HISTORICAL INVOICE / CHECK or other document, it will VOID to the OLD account number and you will need to make a Journal Entry to move the value.
Sorry for the long winded answer, but I hope this helps somewhat with your situation.