Hi Milena
You're right that it's just a matter of changing the order of the <Field> tags. I don't think the value that represents each field is documented (at least, I've not managed to find it), but you can derive it by creating an ESP file and then matching up the contents of the ESP file to the CSV file that it generates.
As an example, these are the values for the fields in the REVENUE table:
520001: VersionName
520003: PeriodName
520005: RespCenterName
520007: RevenueTypeName
520009: CostObject1Name
520011: CostObject2Name
520013: CostObject3Name
520015: CostObject4Name
520017: CostObject5Name
520019: CurrencyName
6107: UnitPrice
6108: UnitsSold
6109: Revenue
Hope this helps
Steve