Here is a very simple example of varying repetition. You won't really see in it the render as the area we're looking at really has no really definition but what the cloud layer is forcing in due to extreme contrasts, but take a look at the last merge shaders preview.
There is clear repetition, but no shape is the same. Adding further warping, translation distances, can improve this method.
Edit: added some test renders with different seeds, and doing another at smaller scale, but will take longer.