I downloaded it, quickly edited a file and in the ASCII window changed some stuff.
Then saved it, and checked it, then changed it back.
It all seemed to work ok.
I am using windows 7 - this program is standalone and does not need to be installed.
You may however, need to run it with administrator privileges depending on your P.C. setup.
I am not familiar with your PIC chip/etc but I would download the hex file to a P.C., edit a copy and when you are satisfied that all is OK, download to the PIC.
Remember - keep a copy of the original file, in case something goes wrong, so you can get back to square one.
Good luck es 73 - Rob