Let's say I'm in the middle of a 72-hour 135F sous vide recipe, and I want to cook some chicken thighs for dinner for tonight.
Does it make sense to put the chicken in the bath at 135 for my normal chicken sous vide time, then finish them using a conventional cooking method (in the oven or on the stovetop), until the inside is fully cooked?
Alternatively, can I turn my 72-hour short ribs SV bath up to 150F for 1.5 hours to sous vide the chicken simultaneously?
You can cook chicken at 135F, or indeed any temperature 131F or up. It will take a while; several hours, as noted in the Baldwin Sous Vide Guide you posted. If you pasteurize it at 135F, you can then later cook it, ignoring the temperature (and only worrying about the texture, etc.), as its already cooked to safety.
If you want to hold it, chill it down quickly, e.g., in an ice bath. Do not remove it from the bag until you're ready to throw it in the oven (to minimize oxidation).
I do not suggest turning your water bath up, as you will end up with well-done shortribs instead of the medium-rare ones you wanted.
I would not do this. While you don't mention an amount of time, the temperature is much lower than what you would need to cook chicken safely. You could easily incubate and multiply harmful bacteria, and while you might kill them off later in the oven...is it worth the risk? Just cook the chicken the traditional way. Here is a good resource for sous vide time and temp: http://www.chefsteps.com/activities/sous-vide-time-and-temperature-guide
