Hi Joao,
Thanks for your post. I'm sorry to have to tell you that the order of columns in the Cable Schedule cannot be changed prior to output.
One solution might be to create a spreadsheet template that links to the Cable Schedule exported by Stardraw Design 7.3 and which shows the data in the order you want e.g. Column A in your template could link to column AC ( or whichever holds the Middle Label) in the exported Cable Schedule. One template like this could be used for all future Cable Schedules.
I hope this is helpful.