I assume you are referring to the amount of yeast in the "Classic" NY Style Dough Formulation Without Oil from Reply 17 in this thread, at http://www.pizzamaking.com/forum/index.php/topic,7499.msg64553.html#msg64553
. With a change in the room temperature where the dough is made, you ideally want to keep the same finished dough temperature. For example, for a finished dough temperature of 80 degrees F, and with a room temperature of 60-65 degrees F and the same temperature for the flour, and a friction factor of 25 degrees F for your Hobart mixer, the water temperature you would want to use is 85-95 degrees F. Since different mixers can have different friction factors, that is something you may have to do some experimentation with to see if you get the desired finished dough temperature with your particular mixer. Once the really hot temperatures arrive, for example, 85 degrees F, the water temperature you would want to use to maintain the finished dough temperature of 80 degrees F is about 45 degrees F.
It is also possible, as I often do in a home setting, to adjust the amount of yeast with changes in the season. Often operators don't like to change the yeast and other ingredients because it is easier and perhaps safer to have their workers who make the dough just change the water temperature. There are also charts that can be used by such workers to tell them the correct water temperature to use to make the dough based on the room temperature and flour temperature. You can see an abbreviated version of such a chart at page 6 of the General Mills brochure at http://www.gmflour.com/gmflour/PDFs/Website%20A49104%20Just%20Crust%20Brochure.pdf
. If you find it necessary to reduce the amount of yeast, I think I would reduce the 1.2% just slightly while adjusting the water temperature based on the room temperature at the time you are making the dough.
It is possible to do the water temperature calculations using a simple calculator but you would first have to determine the friction factor for your particular mixer. If you need help on how to do this, let me know.
EDIT (2/4/2013): For an updated link to the General Mills brochure, see http://www.professionalbakingsolutions.com/water-temperature-chart