I guess it's theoretically possible by loading the file with the file system plugin construct.net/en/make-games/manuals/construct-3/plugin-reference/filesystem
BUT I am almost certain that that's not what you want to do? If you just want to change an old class name to a new one... why don't you just edit the file in the editor?
The files are in the project bar on the right side, doubleclick to open, edit as you wish, ctrl+s.