Using the Recurly python SDK, modify the subscription price not immediately but o the next billing date
According Recurly docs Using the Recurly python SDK you can set the subscription timeframe value to bill_date below a python SDK example.
subscription = recurly.Subscription.get(subscription_uuid)
subscription.unit_amount_in_cents = unit_amount_in_cents
subscription.timeframe = 'bill_date'
subscription.save()
This will cause the pricing update occur on the next billing date and not immediate.