OK, let me clarify.
When you configure the vectorizer, it means that your data is going to be vectorized with that model.
So for example, let’s say you select a vectorizer that embed vectors with 300 dimensions.
Now you want to change to a different model with, let’s say, 1536 dimensions.
You will need to vectorize all your content again, because the vectors came from different models. Even if they had the same dimensionality, they came from different models.
So in order to change the vectorizer, you need to both define the model accordingly and to vectorize all your content again.
So the vectorizer configuration of a collection is not mutable.
Since Weaviate 1.27 version, the generative configuration is now mutable. This means that if you configured your collection to use, for example, cohere as the generative, you can change it to open ai, for example.
gpt-3.5, gpt-4 and so on, is a generative configuration.
Let me know if this helps!
Thanks!