Hi @Javier Llorente Mañas, you can create a connection with the API but you can't change the source's field schema, you can only change the replicated stream. The same as in the UI.
In other words: using the API does not allow you to customize the fields you want to sync, the API endpoint expect the same schema as the source outputs your connection will fail on sync if you try this.
Sorry, you'll have to wait for Airbyte to support schema evolution, this is planned in the next quarters.