Well, this unfortunately is not an easy question to answer. Normally as you increase the temperature in which a species lives, its metabolic rate increases, as do various physiological processes, so in theory, limb regeneration rates should increase as well. Also, since the solubility of calcium carbonate, the mineral that composes the endoskeleton of starfish, is inversely proportional to temperature, it should be more energetically favorable to precipitate calcium carbonate at increased temperatures, so again, in theory, limb regeneration rates should increase as well, as you turn up the heat. But, the story is not this simple. Echinoderms, in general, due to their lack of an excretory system, are typically very sensitive to small changes in environmental parameters and as a result can become very stressed and disease prone following only minor changes in environmental parameters. My guess would therefore be that you might observe a small increase in limb regenerative rates if you increased the temperature a small amount, but too large of an increase would probably just kill the poor starfish. This is a relatively straightforward hypothesis, that, if conducted experimentally under the appropriate controlled conditions, could easily be tested. I hope this helps.