Hello ,
Why you need to change this field?
the ERNAM field cant be changed in MEMASS as its a system updated field, MEMASS is used only to change the fields in mass which you can change in ME22N.
your Auditor wont like to see the change log for ERNAM field as its business critical too.
you can try with some BADI BAPI or Abap program , but i wont recommend to change this field data as far its not VERY CRITICAL.
thanks
kUnal