Event R402 - can it be used to modify the exiting line items?

Hi Experts,

In the function module at event R402, so far I am able to create the new BP line item and new GL line item and append them to t_vkk_doc_id-vkk_doc_r402-n_fkkop and  t_vkk_doc_id-vkk_doc_r402-n_fkkopk respectively.  I am also able to populate some useful value in an empty field in the existing BP line items and modify t_vkk_doc_id-vkk_doc_r402-t_fkkop accordingly.

When the function module is executed, all data are created or populated successfully in t_vkk_doc_id-vkk_doc_r402.  However, when posting happens, the new value that was populated in t_vkk_doc_id-vkk_doc_r402-t_fkkop was missing from the posted document, although the new BL line item and new GL line item were created successfully. 

Is R402 used only for creating new line items?  Where is the best place to modify the existing line items?

Thanks.

Jennifer