SAP Functional, Basis and ABAP Programming Reference Books
Change in Tax

The transaction code to change your tax rate is FTXP.

It is reference to your tax codes. 

Tax rates are always updated with reference to FROM DATE. 

You need not specified the To Date as the current From date becomes the To Date for the earlier rate.
 

Best regards,
SAP Basis, ABAP Programming and Other IMG Stuff
http://www.sap-img.com