how to create custom edit.php

hi
short question: i need do something custom in adminarea – need change post name. how can i edit that file without being overwritten with next update

long version:
im using wp-types and have custom checkbox and i need create when checkbox is selected (and post published) to create postname with (E) at the end of that name, and same thing when i create that how do i keep it from not being overwritten