I created an Infopath form and would like to have a particular field to be set to some default value every time this form is submitted (the field is not shown on the form, user should not have to manually input this field). Is it possible to write values to a SharePoint list via some InfoPath rules? I have tried making a rule "action" ( specifically "set a field's value") but the data connection I have seems to be "receive"-only, so it doesn't actually change the list field I want when I submit the form. Perhaps there are other ways to do it such as with a content-type-specific workflow?
You can create a hidden section and put the fields you desire to promote within there and hide it with formatting rules. Be sure to set the defaults to what you like and when the form is submitted, the promoted fields will be updated.
Alternatively, you could create a workflow on item creation to set the values.