Well, after some fiddling, looks like I somewhat found something that should work (from http://esotericsoftware.com/forum/Changing-Skins-Dynamically-In-Game-1131)...

I modified that snippet to get something like this...

var spineAtlas:Atlas = new Atlas(Assets.getText("assets/spineboy.atlas"), new FlixelTextureLoader("assets/")); var region:AtlasRegion = spineAtlas.findRegion("torso"); var attachment:RegionAttachment = new RegionAttachment("newhead"); attachment.rendererObject = region; var scaleX:Float = region.page.width / nextPOT(region.page.width); var scaleY:Float = region.page.height / nextPOT(region.page.height); attachment.setUVs(region.u * scaleX, region.v * scaleY, region.u2 * scaleX, region.v2 * scaleY, region.rotate); attachment.regionOffsetX = region.offsetX; attachment.regionOffsetY = region.offsetY; attachment.regionWidth = region.width; attachment.regionHeight = region.height; attachment.regionOriginalWidth = region.originalWidth; attachment.regionOriginalHeight = region.originalHeight; skeleton.setAttachment("right-arm", "newhead");

...is supposed to do something like this...

... but crashes at runtime.