I feel the end result is very nicely realized hand.
First up as a refresher, here is the original:


Here is the end result:


Pretty nice huh? Wanna know how I did it? Instructions and tools used below.
X-Acto knife with a nice pointy blade
A slightly stouter razor knife (a slim Olfa) to make some of the tougher cuts
A very fine toothed hack saw blade (I just used the one I use on PVC pipe for plumbing work)
Sand paper (I used 150 grit, but I feel a finer grit like 220 or finer would have looked nicer)
A nail to push out the pin (a punch would work better)
A tiny drill bit to make a new hole for the pin
Of course you could use what ever tools you have or feel comfortable with. I avoided power tools, such as a dremel, because of how fast they cut through this soft plastic.
First push out the pin that holds the fingers in place.

Then I cut off the weapon part with a hack saw blade. Then I made several dado like cuts to clear out the plastic where the fingers will go. I used the xacto and olfa knife to clear out the bits and to smooth out the plastic.


I estimated where I needed to drill new holes, marked them with a nail and slowly hand pre-drilled the holes with the xacto knife. I used a drill bit (by hand) to finish the job.

I used some small nails to test fit the fingers and found that I had to round out the back of the "knuckles" so the fingers could fold from hand to foot.

Then I used sand paper to smooth all the rough razor and saw cuts. I then used a razor scraping perpendicular to the service to smooth/soften the surfaces. The 150 grit sandpaper didn't do the nicest job. I recommend 220, 440 or better yet all three working your way to finer.
I recommend using small nails to test fit and movement before pushing the pin back in. There isn't much plastic left to hold the pin in if it was to bind and be forced going from hand to foot.
Once your satisfied with the movement and clearance, push the original pin back in. As a bonus you could grind the pin just a hair shorter so it will be flush with the plastic.
A few more pics to show off the end result.












And a few more attached to a limb.





Whatcha think?