Table maintanance generator problem

Hi Experts,

I have created a Ztable with 5 fields like Field1,Field2,Field3,Field4,Field5. I have created Table maintenance generator  for that table. I want to disable Field4(created By), Field5(created Date). I have modified in se80 tcode througg screen properties. I want to update the field4,Field5 fileds by sy-datum,sy-uname , How to do without using TMG events? Even TMG events also fine. but my firts preference is without TMG Events....Please give me some sample code. How to Modify the Extract table ?