Yes, as Rob said, we've worked out how to add transparency to any skin texture. Thankfully it's all defined in the same file, and isn't hard to do.
Sadly, semi-transparency is yet to be discovered (and I doubt that this is possible at the moment).
I don't think it is at all possible to have semi-transparency. The way that it works doesn't allow for it - the program looks for pixels with a certain RGB value and deliberately avoids loading those pixels. For semi-transparency, it would need to have a certain colour defined to not only represent a semi-transparent pixel, but also what colour this pixel should really be, and what percentage of transparency it should be. I highly doubt this can be added into the program, especially as nothing in the game is semi-transparent (there must be a better term for this than that). But hey, if someone can prove me wrong, great!
Unfortunately I was too busy today to update this tutorial (I briefly popped in and out but haven't been able to just sit and type), but I will aim to do it as soon as possible.