In short, my question is this.

I used to download software from -Devel and -Testing but got errors with the Fremantle and thus returned to the Stable/Extras. Now I'd like to go back to the -Devel/-Testing but I'm facing a minor problem.

In order to avoid re-flashing the whole device I'd like to know that can I add another installation of Fremantle to the device? I'd have this way two installations, one for testing and one for stable. This would be perfect for me, since I could just remove the testing installation and merge it back to the stable (which I'd need instructions though, I pretty much suck when it comes to Linux and partitioning).

So, would this be possible? I assume though that I'd need to install multiboot, which ironically is from -Devel, to the stable partition.