How can a "random" number be maintained with mass maintenance?
Mass maintenance usually distributes one number into several targets or can built a target value by reference.
But looking at those numbers,
ABC001 12345
ABC002 43984
ABC003 30493
you understand mass maintenance probably as copy & paste of values into an input screen with several rows, this is not supported here. you need to upload such values, and for this you can use LSMW or SECATT or Batch Input recording.