Changing amount for Stripe 'charge later'

So there is an option when adding stripe to run immediately or run manually later.  When it sends us an email it has a link to run now.  When you click it, the credit card is charged.

1) Is there anyway to do a pre-authorization to make sure funds are available before we do service? Or is stripe already doing this?

2) Is there anyway to change the amount of the purchase if the customer adds on a service after the fact?

Looks like I can go into my stripe account and just do a manual entry if the amount is different. (Does this affect question 1) if it is pre-authorized.

1) Is there anyway to do a pre-authorization to make sure funds are available before we do service? Or is stripe already doing this?

The answer is no. Our 'charge later' feature simply sends the user's payment information to Stripe and saves it on our server as a token. When you are ready to do the charge, our system uses the same token to proceed with the transaction charge.

2) Is there anyway to change the amount of the purchase if the customer adds on a service after the fact?

Currently no, there is no way to do that.