When you with maintaioned condition record for "tax code" in FV11,the keys combination trigers from your condition table which assigned to access sequence which in turn itself access sequence
assigned to tax condition type!
So if needed creates a new condition table 997 with as keys combination Country,Vendor,Plant, Material,Tax code and Region( or else also you can use access sequence JST1 or MWST in t.code: OBYZ).Now create new access sequence(ZOWN) and assign new condition table(997) and then
assign new access sequence(ZOWN) to all tax condition types in t.code: OBYZ.
As needed,now create tax code (FTXP) and maintaion TAX RATE in condition record in t.code:
FV11 with tax condition type for your new condition keys for Country,Vendor,Plant,
Material,Tax code and Region with for a Validity Period.