It sounds as though you would prefer to not have to do this at all.  If you are just trying to update the status, have you considered removing the Require Acknowledgement from the customer (Maintain Customer / Sales Order tab) and then all orders will immediately go to a status of Open?

Is actually the other way around...we want to keep this feature on for non-edi partners. but want to automate this for our sales. Where our system automatically sends the order ack at the end of the day (say 4pm)

Is actually the other way around...we want to keep this feature on for non-edi partners. but want to automate this for our sales. Where our system automatically sends the order ack at the end of the day (say 4pm)

This would require you to build a customization if you wanted to do it using the same mechanism through document transmittal of Sage 500 ERP.

If you truly want it to be automated you should consider a tool such as KnowledgeSync (by Vineyardsoft), TaskCentre (by Fisher Technology) or one of the many other options that are available for this type of activity.  These tools can be used to generate notifications to both internal resources on your team as well as to external resources (customers/vendors/etc).  We have clients that send Invoices, Ship Notifications, Payment Advices (for ACH payments) using these tools.