Hi Wataru,
That information is not readily available and I will have to do some checking to find it. Basically the offset correction is done first with the gain scaling afterward for the final correction. Generally we do not advise any manipulation of the data in these registers as this can create additional error especially if the gain correction is taken beyond the limits of the design.
You might ask why the registers are available for reading and writing? The answer is there is only one set of registers and a number of input combinations. Each of these combinations may have a different result. These results can be stored somewhere else and then restored to the ADS1240 as needed.
Best regards,
Bob B