I have done in-bottle pasteurization to arrest fermentation when making a sweet cider. I prefer dry cider though, which doesn't require pasteurization since all the sugars are fermented out.
Are you trying to make a dry cider or a sweet cider? If you ferment to full dryness (1.000 Gravity or below), and then only add enough additional sugar at bottling for your desired carbonation level, then there is no need to pasteurize.
The process is a bit of a pain. Safety precautions are important since the process creates the possibility of flying glass shards. I have never had a bottle explode, but it can happen. Wear safety glasses and a thick, heat and water resistant apron.
Process: Monitor bottles until desired carbonation level is reached. The easiest way to do this without constantly popping bottles open is to fill one or two plastic soda bottles in addition to your glass bottles. You can then squeeze the plastic bottles without opening them to feel how much pressure there is. When if feels right, pop open one of them and test it. If not carbonated enough yet, that's why you have more than one. Once the desired carbonation is reached, drink the plastic bottles. You cant pasteurize in plastic.
Prepare a hot water bath in a large stock pot on the stove. Put enough water in so that the water level comes to 1 inch from the top of the bottles with the bottles in the pot. To measure this, put the bottles in, fill with water to the desired level, then remove the bottles and heat the water. Water should be heated to 180F (this allows for some cooling while keeping everything at or above the necessary temperature). Do not let the water boil, if you do you will need to let it cool to the desired temp.
Once water is correct temperature, turn off heat, then put bottles in the pot and cover the pot. Wait 10-15 minutes, then remove the bottles. Be careful, as the bottles will be quite hot! Set the bottles on the counter to cool to room temp. They are now pasteurized.
Bottles: I used 500ml EZ Cap bottles, with the flip-top cap. The nice thing about pasteurizing in these is that the cap acts as a pressure-release, venting a little if the pressure in the bottle gets too high.
My advice: Don't bother with sweet ciders. Go Dry and you will never go back. Much more complex flavors. I have found that dry ciders seem to appeal to everyone, including beer drinkers. Sweet ciders appeal more to people who like mixed drink cocktails.
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