If you want to customize Shelley, open up a conversation, and ask the agent to change itself. It will do so. When a new version of Shelley ships, it rebases your customizations onto the latest version, so your changes always carry forward.
The traditional approach to software customization has been configuration and plug-in architectures. With the advent of coding agents, a third way is viable: edit the code. The tool exists to serve you, so treat it like a wiki, slap an "Edit With Shelley" ribbon on it, and go to town.
Give customizing Shelley a shot! When you've got features that can stand the test of time, pop into our Discord, and let us know.