One way to do it would be to load the field names into QlikView and allow people to select what they want to load. Then, you can build the list of fields for your LOAD statement in a variable and use the variable in the script.
You may have to use Partial load, or apply other tricks to avoid losing your selected values at the beginning of the reload process. Or, you could have two documents - one document with the metadata (field names) and the other document that actually loads data into QlikView.
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I don't think there has to be an option for your users to influence the load execution only to let them decide "which column is shown in the Orders table".
There are many exmaples in this community to do so without reloading:
hope this helps