Mass update of customer tax category

Hi,

I am trying to carry out customer tax category mass update.

I tried using XD99 and MASS- but both did not work.

Although i gave the correct selection criteria, it did not select the records that i wanted.

1- Please let me know of any alternatives?

2- I tried XD99 and MASS - By Selecting tables KNVV and KNVI and select the field TAXKD

Is that correct?

Thanks in advance.