You could write it in a text editor,
same as you use for program source code editing.
What kind of data is it that you want to write into the EEPROM?
The .hex file is a text file with hexadecimal numbers.
There is a checksum at the end of each line.
It is a general format that is used for many microcontroller types.
See Wikipedia for description for how it is put together.
There should be open source and freeware programs around to manipulate contents of .hex files.