with the rexxer dealer unit I have, if I flash it I can reflash it at a later date without using another credit.......
So once I pay my AU$400 I have all the subsequent flash updates I can eat?
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the siemens ecu file can't be read out of it without getting destructive I believe.
Yup. Same with the Rexxer User unit.... it was originally intended to be able to upload the stock file from the ECU to rexxer device before downloading the new reflash file.... but never worked out that way in the end. Which is why IMO its a good idea to have a copy of the stock ECU mapping kept aside... just in case.