Check the datatype of the column which contains the date format. Why do you want to take the dump of the Source table? There is no need to change the format in the Source table. All you need to do is convert the date in the appropriate format in the Query transform so that the date is outputted in the correct format(e.g. Source Date format is MMDDYYYY and the required Target Date needed is DD-MM-YYYY)
Refer to_date() function in the reference guide
http://help.sap.com/businessobject/product_guides/sbods42/en/ds_42_reference_en.pdf
Regards
Arun Sasi