Soldering the ten inches back on the tip will probably improve reception, depending on the overall length of your antenna (I can't tell how long it all is from the picture).
I'm guessing if it was designed to be used with the radials, having the entire length of the mast would be preferable. Looks like its got a loading coil. Definitely is designed to be used with the entire length of the mast.
I don't see why you couldn't use a tuner with it. To a tuner, whether it's wire or a telescoping whip, it's just a length of metal. I'm not sure exactly how much a tuner will help, being that it looks like a tuned antenna -- but there's no harm in trying it.