Note: If eg CR2 file exceeds ~100 Kb, 'Notepad' may become unstable or 'hang'. If so, open file with eg Wordpad, which lacks such constraints...

I ran into this 'hacking' mis-exported OBJ files which had 'many' material regions, but only one (1) material name...

( And, d'uh, make a 'safety' copy of original file, to be sure, to be sure... )

There are also 'Classic' utilities such as Phil_C's wondrous CR2 editor...