Craft Commerce - Purchasables and multiple gateway accounts
You wouldn't need to dynamically change the Stripe credentials on the Stripe payment method, rather it is more likely you would set up a seperate Stripe payment method for each Stripe account. 

It is a little known feature that you can set up more than one payment method per gateway with different credentials. 

You could then hard code the payment method ID to the relevant teams payment screen (or set it on the cart before they get to the payment page). You could even store the payment method ID in that teams entry. 

Hope that helps for the initial question.