How can I calculate the tax in Receivables on a specific date?

Hello Experts,

As a result of the upcoming economic stimulus package, tax rates in Germany will be reduced from July 1st. I would like to write offers today for orders to be realized in July. These should include the reduced tax rate. I can do this in Order Management, but when I book the orders, I get again the non-reduced tax rates in RA. I hoped to achive this via the SHIP_DATE_ACTUAL in the RA_INTERFACE_LINES_ALL, but it doesn't seem to work. The entry in this field seems to have no influence on the tax calculation. Do you have any idea how to