There's a Cancel and Return button or link at the bottom of the PayPal Checkout page. Other than the customer using the Back browser button, there no additional features or options available to do what you have in mind.
The PayPal Checkout Screens you see are limited to changing the scheme and/or allowing you to display a business logo graphic (Business Accounts only) and/or changing the text for the "cn" variable value and/or changing the text for the "cbt" variable.
The "cn" variable value is a the Label that appears above the note field. This value is not saved and does not appear in any of your notifications. If this variable is omitted, the default label above the note field is "Add special instructions to merchant." The "cn" variable is not valid with Subscribe buttons or if you include no_note="1". The "cn" variable value is limited to 40 characters.
The "cbt" variable default value is displayed as a link which says "Return to Merchant". If you are utilizing Payments Standard and have a return page set up, you will find that your non-PayPal members will need to click on the "Return to Merchant" link to be directed back to the return page. In some instances this may not be the best way to alert customers that they can return to your website by clicking on the link. The good news you can change the value to what ever you would like. The "cbt" variable value is limited to 60 characters and only takes effect only if the return variable is set.
That's all you can do. Note, (Payments Standard is a free product.)
If you want total control over your checkout screens, you would need to use Payments Pro. Pro does not redirect customers to the PayPal Checkout Screens. The customers remain on your web site thru the entire process therefore you can design any checkout experience you have in mind. (Payments Pro however, is not free, it costs $30 a month.)
