I emailed an edited file back to you awhile ago.
In Hackman, you should just be able to click on save (floppy disk toolbar icon) or use the hotkey ctrl+s to save any changes. There may be a function to open files in read-only mode, but I don't think that is set by default.
In any case, you would need to browse to the folder in Windows Explorer and rename the data.001 file to data.000 for the game to load it (perhaps rename the original file data.bak first).
If you are changing the first byte of the coordinate, then 99 to 83 is not very far (about 1/5 character height; 00 to FF would be about 2.5 times the character height). Modifying the second byte by that much would be very far (50 times the character height).
