Ho to set a single cell in alv Webdynpro Abap

I am trying to edit a single cell on lead selection. here the steps i did to achive this.

1. I added a Attribute READ_ONLY  inside my node of type WDY_BOOLEAN.

2. i am conditionally making this Attribute - READ_ONLY = 'X'.

3. i am binding my node with new values.

4. for ALV here is the code i have added.

DATA :lo_cmp_usage TYPE REF TO if_wd_component_usage,

        lr_column    TYPE REF TO cl_salv_wd_column,

        lr_table_settings TYPE REF TO if_salv_wd_table_settings,

        lt_columns TYPE salv_wd_t_column_ref,

        ls_columns TYPE salv_wd_s_column_ref,

        lr_input_field TYPE REF TO cl_salv_wd_uie_input_field,

        lo_interfacecontroller TYPE REF TO iwci_salv_wd_table ,

        lv_value TYPE REF TO cl_salv_wd_config_table.



*Taking reference of the Component Usage

  lo_cmp_usage =   wd_this->wd_cpuse_cu_alv( ).

  IF lo_cmp_usage->has_active_component( ) IS INITIAL.
    lo_cmp_usage->create_component( ).
  ENDIF.

  lo_interfacecontroller =   wd_this->wd_cpifc_cu_alv( ).
  lv_value = lo_interfacecontroller->get_model( ).

  CALL METHOD lv_value->if_salv_wd_column_settings~get_columns
    RECEIVING
      value = lt_columns.

  LOOP AT lt_columns INTO ls_columns.
    lr_column = ls_columns-r_column.
    CASE ls_columns-id.
      WHEN 'USR_ACT_RT'.
        CREATE OBJECT lr_input_field
          EXPORTING
            value_fieldname = ls_columns-id.

        lr_column->set_cell_editor( value = lr_input_field ).
        lr_input_field->set_read_only_fieldname( value = 'READ_ONLY' ).

    ENDCASE.

  ENDLOOP.



  lr_table_settings ?= lv_value.

  lr_table_settings->set_read_only( abap_false ).

  lv_value->if_salv_wd_column_settings~delete_column( id = 'READ_ONLY' ).

but instead of changing the particular cell where i have marked READ_ONLY = 'X' it is changing whole column 'USR_ACT_RT'  data as editable .

If anybody can  please help ASAP