I don't know the extent to which Hasbro could or would consider suing over these kinds of things, but reprolabels has operated for years doing sticker decals and Hasbro either doesn't care, or hasn't cared enough to get them shut down.heh, looks as if i was mistaken regarding copywrite infringement.
Given that these companies are providing services that can only increase the sales of these toys (i.e. they aren't providing bootlegs that can cut into Hasbro's or Sideshow's profits), I couldn't imagine why they would take issue with it.