Issue using BADI FI_INT_CUS01

Hello Experts,

I want to change the tax code per document while using the tcode FINT. But i cant find a way to do this using BADI FI_INT_CUS01. I am using INT_ADD_ITEMS method achieve this . In this method there is the parameter CT_T056U_EXT where which i am trying to change the MWSKZ. But i am not able to find a relation between CT_T056U_EXT and CT_ITEMS. In CT_ITEMS for every document number i would like to look into BSEG and find the tax code and substitute the same in MWSKZ of CT_T056U_EXT . When i have more than one tax code to substitute and CT_T056U_EXT comes with only one line item , i am clueless how to add more tax codes .

BR.

PD.