The data fields you can use in your Notification Template are based on the Screen you select for your Notification Template:
Since this Notification Template is based on the Sales Orders screen, the fields you have access to depend on what is available on that screen.
I don’t think they are meant to be re-arranged in the data fields view, however if you want more control over what is or is not available (as well as a simplified tree layout), you can try using a Generic Inquiry as the screen for your Notification Template instead of a data entry screen like Sales Orders:
If you opt for using a Generic Inquiry, you will get access to all the fields that were exposed under the Results Grid tab of the Generic Inquiries screen:
I don’t have much experience with the notification templates but I believe those are pulled from the views defined on the graph of the screen. If you are trying to add a specific field I would guess it only pulls fields with a PXUIField attribute.
That being said you may be able to use (([ViewName].[FieldName])) even if the field is not listed in the insert panel.
I’m not sure I completely understand your question, but let me offer you this.
You can change the screen the Notification Template is tied to, however you will always only have access to the fields in that screen. If you are looking to combine the available fields from two or more distinct screens, I don’t think that is possible.
If you want a completely customized fieldset in your Notification Template, the only way I know to do that would be to create a Generic Inquiry and explicitly expose the fields you want to include.