How to switch my Stripe account without breaking existing subscriptions

I use Pabbly Subscription Billing with Stripe as my payment gateway. My current Stripe account is registered in Germany. I have now created a new Stripe account in the USA (for my US company), and I want to move to the new account.

I have active subscriptions from existing customers that renew automatically. I do not want any renewal payments to fail.

My questions:

• 1) If I replace the Stripe API keys in Pabbly with the keys of the new Stripe account, what happens to my existing active subscriptions? Will their renewals still work, or will they fail?
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• 2) Stripe offers to migrate my customers and their saved cards from the old account to the new account, keeping the same Stripe customer IDs. If I do this migration first, will Pabbly then be able to charge renewals through the new Stripe account?
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• 3)Is it possible to connect both Stripe accounts at the same time, so old subscriptions keep renewing on the old (German) account and only new customers use the new (US) account?
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• 4) What is your recommended step-by-step process for switching Stripe accounts without losing any renewals?

Thank you!