Edit form field that has been autopopulated

I used a script to autopopulate physical and mailing address based on a drop-down selection from of location's name.  If there is an exception for the mailing address, I would like to delete out what was autopopulated and manually type in the correct information.  However when I tab to the next field, the autopopulated data comes back and what I typed in disappears.

Thanks for your guidance all!