Updating data in from a grid without overwriting the ids

I am trying to save data that is updated in an editable grid, but when I save the data - everything saves correctly except that the ids. Existing table, ABC_Customer has id, name, accountNum, fiId, effectiveDate. I have a read only grid that the allows the user to select which rows to update. the selection of rows is then displayed in a new grid that has editable data. 

This is a follow-on question related to a previous post of mine, but since it's a new topic - thought I'd create a new item. Anyway - this is what I hav

UpdatingCdt.txt
        a!dropdownField(
          label: "Account Number "&fv!index,
          choiceLabels: {ri!selectedAccount_cdt.accountNum, ri!newAccount_cdt.accountnum},
          choiceValues: {ri!selectedAccount_cdt.accountNum, ri!newAccount_cdt.accountnum},
          value: fv!item.accountNum,
          saveInto: {fv!item.accountNum,
              if(fv!item.accountNum = ri!newAccount_cdt.accountNum,
              a!save(
              target: ri!updatedCustomerAccount_cdt.fiId, 
              value: ri!newAccount_cdt.fiId
              ),
              a!save(
              target: ri!updatedCustomerAccount_cdt.fiId,
              value: local!selectedRows.fiId
              )
              ),
              if(fv!item.accountNum = ri!newAccount_cdt.accountNum,
              a!save(
                target: ri!updatedCustomerAccount_cdt.effectiveDate, 
                value: today()
              ),
              a!save(
                target: ri!updatedCustomerAccount_cdt.effectiveDate,
                value: local!selectedRows.effectiveDate
              )
              ),
              if(fv!item.accountNum = ri!newAccount_cdt.accountNum,
              a!save(
                target: ri!updatedCustomerAccount_cdt.accountNum, 
                value: ri!newAccount_cdt.accountNum
              ),
              a!save(
                target: ri!updatedCustomerAccount_cdt.accountNum,
                value: local!selectedRows.accountNum
              )
              ),                                  
              a!save(
                target: ri!updatedCustomerAccount_cdt.CustomerId,
                value: local!selectedRows.CustomerId
              ),
              a!save(
                target: ri!updatedCustomerAccount_cdt.aipCode,
                value: ri!newAccount_cdt.aipCode
              )
          },
          required: true()
        ),
e for my dropdown component. All the data that is updated is saved, as expected, except the CustomerId values. The first CustomerId is reflected on pv!updatedCustomerAccount_cdt - for all records updated. If there are 3 records being updated to the new account information - I want the CustomerIds to be the ids associated with the records to be updated. How do I do that? I'm sure I need to include some sort of index on the selected row but I couldn't find anything in the documentation or previous discussions on how to do this. 

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