I would worry the effect this may have on your credit rating if anyone catches you at it, together with possibly more serious effects. This could potentially be considered fraud. Altogether it seems much more sensible to simply live within your means and pay off your credit balance each month.
...it seems much more sensible...
This is the "ridiculous munchkin ideas" thread, not the "sensible advice you've already heard" thread.
This could potentially be considered fraud.
A more pertinent worry. Especially with cards that give a percentage of each purchase as "reward points" or something, I'd be worried about this.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.