First of all, no they won't. Worst case it'll be returned to Apple and refurbished or they'll put it out as open item and get reimbursed by Apple for the difference.
Second, THEY SET THE RULES. Those rules are there to make sure you don't have a lot of upset customers complaining about buying things they use for a day and decide they don't like [or that don't suit their intended usage]
Third, WHO GIVES A ****??? They're a corporation. They sell your information and purchase history for money on the side. YOU ARE A PRODUCT TO THEM, not a person. You're nothing but profit margin. They're gonna keep their high turn around profit policy, their "always over on hours" philosophy, and their "minimum wage only until we replace you" pay grades.
Caveat Emptor works both ways.
O/P: I think what you're doing makes a lot of sense. This way you can find out sooner rather than later whether or not the new macbook fits your needs or not, and you can then know in advance if you're going to return one of them or BOTH of them. [or neither of them, who knows ^^]