When we use proxies, we actually use proxy cards and not counterfeit/copy cards. As an example, when I just had the one core box to play and I wanted more Hand of Bims I took 3 firebrand imps and made sure my opponent knew that when my priestess deck played an imp, it was really a Hand. I can see where your method would look better, but it seems a lot of work and murky in terms of copyright stuff.