In the following code snippet, you will understand how to modify internal table of type standard with non unique keys.
READ TABLE lt_internal_table WITH KEY field1 = field1_value ASSIGNING FIELD-SYMBOL(<ls_record>)
<ls_record>-field2 = `field2_value_modified´ .
Now the internal table will be updated with the modified value. So we have here modified the internal table without using modify statement.