It would be a good idea to work on a copy of your site first since you have updated the cart. You should reapply the checkout server behaviors. You can either open up your checkout, confirm, and pp_confirm pages and update the individual PayPal checkout server behaviors on these pages or you can backup your current checkout pages into another folder and run the checkout wizard again to crate a new set of pages for you.
I would suggest just updating the server behaviors, it is less involved and should give you the correct result. The server behaviors that you will need to update are:
Authentication for PayPal Express checkout (checkout page)
Get Payer Profile for Express Checkout (pp_confirm page)
Process Transaction with Express Checkout (pp_confirm page)
eCar local checkout (PP_Direct_Payment) (confirm page)
You can just double click on them to edit, the setting should be fine but you should double check them along the way, then finish the server behavior to have it write out the newly updated files.