Does anyone know if it is possible for the seller to change,
directly from an order, the payment methods from cash on delivery, to bank transfer, or from paypal to bank transfer?
With VirtueMart 3.8.4
This can do what You want.
https://www.daycounts.com/shop/plugins/finalize-order-plugin (https://www.daycounts.com/shop/plugins/finalize-order-plugin)
Jörgen