Answer
There's no built-in per-document choice through the Message Class configuration alone — this requires a small customization. The practical approach: add a Custom Menu item that triggers printing directly (bypassing the standard EDI-send flow), giving users a genuine choice between the standard RMB Send option (still available as-is, sending via EDI) and the new custom menu's Print option, for exactly the documents where a case-by-case choice is needed.