The 2nd argument to the GetValueAt() method is for delimiters, not status. The status is returned in the 3rd argument. The correct syntax for what you were trying to do is:

Set tOBXText = pOutput.GetValueAt("ORCgrp(1).OBRuniongrp.OBXgrp("_i_").OBX:5", ,.tStatus)

Note the additional comma before .tStatus.

An UPDATE example:

UPDATE Sample_DB.Greetings SET Greeting = {fn CONCAT(Greeting,' World')}

Another option would be to "chain" a 2nd DTL in the Send action for each sender that has its "Create" setting as Existing. It would handle the evaluation and population of the ordering provider. You wouldn't have to touch a bunch of DTLs, but you'd be modifying a bunch of routes.