Change workflow container data from parent ID

I have requirement to change the workflow future levels of 'approvers' including current level.

I am calling the FM SWW_WI_CONTAINER_READ first then i will call the below FM to change the container data.

SWW_WI_CONTAINER_MODIFY is giving me runtime error i.e. conversion error. I am trying to modify using the workflow ID.

SAP_WAPI_WRITE_CONTAINER is giving me lv_return_code = 1, here i tried for both parent ID and workflow ID.

So not at all i am able to modify container data.

Please help me.....and suggest how to modify....