Hi,
If you're asking that, I suppose that it's because you would like to just authorize the transaction during the checkout so that you know that the client has the funds, but then capture the funds when the parcel is ready to be shipped. Is that right ?
Changing authorize.net plugin to do the authorization only during the checkout should be a matter of changing one line in the plugin.
But, then, capturing the payment when the order status is changed will require to create a new function in the plugin to contact the payment gateway as well as adding some code on the order notification function to save the transaction id in the order information so that it can be used in the capturing request to authorize.
You can do it, now it's not just 2 lines of code to add... Otherwise, we would already have added them.