Here's an easy, yet tedious method for rescaling bones and images:
1) Start off with your standard/large images and bone definitions. Let's assume they are in the directory named "Dragon-Plain".
2) Select your scale rate. Example: 0.18.
3) Create an image directory for your scaled images. Let's assume "Dragon-Plain-Small".
3) Scale your standard images according to your scale rate. Something that is 256 pixels wide now becomes 256 * 0.18 = 46 pixels wide. I use GIMP for rescaling.
4) Do not change the image names. Instead, just store these smaller images to the "Dragon-Plain-Small" dir.
5) With Spine closed, rename "Dragon-Plain" to "Dragon-Plain-Large". Rename "Dragon-Plain-Small" to "Dragon-Plain"
6) Launch Spine. The bones will still be in their standard places, and all the images will be small and appear disjointed. Don't panic.
7) Select the root bone. Scale the X & Y to 0.18
8) EVERYTHING will shrink down... even the images.
9) Lock the image and bone settings.
10) Go through the structure bone by bone and change the scale from 0.18 back to 1. You'll notice that before doing this, images have a scale of 1, after doing this, images have a scale of 0.18. You may have to adjust the length of the bones points to improve their appearance. The locking will prevent any joints you've created from moving around. Yes. This is tedious and sucks.
11) Go through the structure image by image and change the scale to 1.0. Be sure to do this for multiple images in each slot. Yes. This is also tedious and sucks.
Enjoy your new scaling without having to redo any animation or create any new bone scalings.
Here's a quick video showing a couple of the steps:
If there's an easier way to do this, I'd be interested to know!