Hi mrdl,
Unfortunately that's not possible. Well it's possible, but we modify thousands of lines. So probably it will take you a fair amount of hours to catch up. Also, the amount of errors/bugs will be increased due to lines not changes or mistakes.
If you want to modify osclass you could do your own plugin, or submit the changes to the core (if they're interesting for other people as well) and we could end including them into the "official" code.
Thanks