It's an interesting concept, and I admit it would be pretty cool, but I don't think it would be that possible. The DS doesn't have an operating system, so once a game has taken over, it has full control over the hardware, and anything previously run is cleared. While perhaps a library could be created for homebrew developers to add the capability to their programs, you wouldn't be able to use it on anything that wasn't compiled with support for it.
The only other thing I can think of is something like Nitro Hax with official cartridges, but I highly doubt you'd be able to create an Action Replay DS code that would do something like this.
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