As the developer of content for a project using Git, you should create your own private copy, or clone, of a repository to do your development. This development repository should serve as your own work area where you can make changes without fear of colliding with, interrupting, or otherwise interfering with another developer.
Furthermore, because each Git repository contains a complete copy of the entire project as well as the entire history of the project, you can feel free to treat it as if it is completely and solely yours. In effect, it actually is!
One benefit of this paradigm is that it allows each developer complete control within her working directory area to make changes to any part, or even to the whole system, without worrying about interaction with other development efforts. If you need to change a part, you have the part and can change it in your repository without affecting other developers. Likewise, if you later realize that your work is not useful or relevant, you can throw it away without affecting anyone else or any other repository.
As with any software development, this is not an endorsement to conduct wild experimentation. Always consider the ramifications of your changes, because ultimately you may need to merge your changes into the master repository. It will then be time to pay the piper, and any arbitrary changes may come back to haunt you.
Faced with a wealth of repositories ...