The best solution would be to speak with the team that manages your ordering system and ask them to include the client names you want in the export. This should be a very simple task for them.
If that's not an option then a simple way to do this in Excel would be to keep a look up table on a spare worksheet. It would contain the client codes and the corresponding Client Names, eg.
Code:
Code Name
Brian012 Briancleaning012
Ber01 Bervaille01
Then, in a spare column in your export worksheet, you can do use VLOOKUP() to pull in the correct name for each code. At that point you can either leave the codes and the names in the export, or you can copy > pastespecial values the names over the codes.
It's also possible to automate this using VBA but, considering both that it would be quite a steep learning curve and that the manual VLOOKUP() method is pretty quick once you've set up the look up table, it's probably worth putting to one side for now.