MarketPress - 2 questions

A couple of questions regarding MarketPress.

When choosing a product to have an external link, the button on it says 'Add to Cart', but it just takes the user to the external link. Is there some way to have this say 'visit external link' or something similar?

Even better, would be to have the product added to the cart, maybe listed below the products paid for on the site, and have the links to purchase next to them on there. That way, users would see the amount being spent and then be able to organise their shopping.

When the error message comes up, for example:

Sorry, there is not enough stock for -2. (Wool Blanket remaining)

Is it possible to change that? It doesn't seem to make sense, but it would also be good to be able to edit it, to say something like:

Sorry, there is not enough stock for Wool Blanket remaining, please contact us to be informed when it becomes available

And that could then include a link.