assign a sentence in header vendor text in PO

Hello all,

in case of limit item SC, i want to add automatically a sentence in the header vendor text in PO if the expected amount is less than the limit amount.

I created a new method in badi 'BBP_PO_CHANGE' and i used the parameter ct_longtext as below.

DELETE ct_longtext WHERE  tdid = 'HTXT'. " Clear vendor text

         APPEND INITIAL LINE TO ct_longtext ASSIGNING <fs_text>.

         IF <fs_text> IS ASSIGNED.

           <fs_text>-guid = is_header-guid.

           <fs_text>-tdid = 'HTXT'.

           <fs_text>-tdspras = lv_lang.

           <fs_text>-tdline = text_itab.

*          unASSIGN <fs_text>.

         ENDIF.

Here is my problem: the sentence is displayed only when i edit the PO. But i want it to be displayed automatically once the PO is created.

Couild you help me .

thanks,

Meriem.