The extensions are not mandatory. If Terorrism is added then you're not taken to any further pages. - it's simply added to the product.
The parametric weather 'extension' only appears if it's an event where 'adverse weather' is an exclusion (see rating table guidance) - generally outdoor events not covered.
However, if Parametric weather is added, then you are taken to the parametric weather pager 'select perils' (as shown in whimsical flow.