Changing the account you have already set up for a specific payment method is not recommended. Each payment method ties into your MemberMouse billing with keys that are specific to your account. If you change the account when you have active subscriptions, the current subscriptions will go into overdue status on their rebill date.
If you have already changed your account, and are using a card-on-file payment method (e.g. Stripe), you can correct this by replacing the current keys with the original account keys. If this is done within the Automated Overdue Payment Handling period for an account, then at the next scheduled attempt, the billing will proceed as normal.
For accounts that use an outside payment method like Paypal, or card-on-file methods which have already completed all rebilling attempts, the current subscription will need to be purchased again to restart proper billing.