We have a large archived batch of invoices that we copy and send out each year to our clients. This year we wish to change the terms of payment. Is there a method of changing all the terms on all the invoices at one time?

If there are a LOT, and we are talking about Adagio Invoices, then it might be worth while exporting the invoice batch, changing the terms and then importing the resulting file into a new batch. This will be fiddley and might take several attempts to get it right. The structure of a import in Invoices is complex. Make sure you read the Help file for details about the available formats.