Yes, you can swap a subscription for another one that has the same cadence and items but a different price. To do this, you would use the UpdateSubscription endpoint of the Subscriptions API. In the request body, you would provide the ID of the new subscription plan in the subscription_plan_id field.
However, please note that the new pricing will only take effect at the start of the next billing period. If you swap the subscription immediately after it’s created, the new price will not be charged until one week later (since your subscription has a weekly cadence).
Regarding your question about static pricing, yes, you can use static pricing for catalog items. When you use static pricing, the price of the subscription plan overrides the price of the catalog item. So if you swap a subscription to a new plan that has static pricing, the price of the new plan will be charged at the start of the next billing period, regardless of the price of the catalog item.
And yes, you can only swap variations of the same parent subscription plan. If you want to change to a completely different subscription plan, you would need to cancel the current subscription and create a new one.
This answer was reviewed by @Bryan-Square.