How to change drupal commerce status message?
You need to find the rule called 'Display an Add to Cart message' and edit it.

You'll see there is a related action in there called 'Display a translatable Add to Cart message'.  In mine, I've even added a second action that takes folks to my cart immediately after adding an item:



In any case, what I would do is delete that specific action and then Add a new action instead.  From the 'System' section, choose 'Show a message on the site'.



Then, in the 'Value' field of that action, you can add whatever message you want and you can add html in it as well.  So you can add something like:

Ready to &lt;a href="/your_custom_cart_url"&gt;checkout&lt;/a&gt;?


Let us know if this worked for you...