Is it possible to change the customer on the Invoice posted to a closed period? The Allow Non-GL Changes is enabled. Although the SAs state that it's possible, when I actually do it, I get the error that we get when changing a GL impacting field of a posting transaction in a closed period.

The customer is GL impacting so you can’t change it It impacts A/R

Changing customer on invoice created from sales order is bad idea too.

Thank you. There are SAs staying that it's now available for editing but it isn't when I tested. Luckily, the invoice is stand-alone.

You can get support to enable changing entities in closed periods.

Thanks, @michoel