The only reason they can't be edited is because they are in the C:\Program Files (x86)\ directory tree.
The best way to edit these would be to copy them out somewhere where you will maintain them in the future, edit them there, save them there, and then copy them back over the original files. You will need Administrator rights to copy them back of course.
No doubt updates and upgrades to MC will overwrite these files, so an improvement to the above would be to create a "C:\Program Files (x86)\J River\Media Center 21\Data\Custom Resources" directory and copy your modified files into that directory. I believe that MC will then use the CapitalizationAllCaps.txt and CapitalizationExclusion.txt files in this new directory, instead of the files in the original "Default Resources" directory. No need to delete the original files in the original directory. You will still need to maintain the files outside that Custom directory, since they are in a directory protected by Windows. But that is good practice anyway, as you will have a backup of your modified files.
The contents of the files seem pretty straight forward, so I' sure you aren't having trouble with that.