As for hacking the counts, I think they'll be stored on the internal NAND so it's likely not possible until the firmware's opened up. However, I think I'd probably be sick of the Resi demo after 10 plays, let alone 30. The game is fine, but the demo is very short, which makes you wonder why they put a limit on it in the first place. I mean, it's not exactly like you can complete the game or get the same satisfaction as playing the full version.
My kids enjoy the Cooking Mama demo, but they have enough Cooking Mama games on DS and iPhone for it not to be that much of a big deal when the demo's gone. I'll probably wait until the price drops before buying the full game.