A better way to do it is to use a cooler, put an airstone in it to aerate the water, place it in a cooler part of the house for a day or two, with the lid shut. Check the temperature, and when it's resonably close, acclimate normally. I tcould take a few days, depending on the temp, also, keep the lid on the cooler as closed as possible. You can't close it all the way, but you want to trap as much cold in there as possible. Also, you will have to use a large enough cooler.
Fish in the wild often times go through rather drastic temperature swings due to thermoclines. I have seen thermoclines in the ocean that showed up on depthfinders very well, the thicker the line the more drastic the thermocline. We guistimated some of them to be a difference of 20-30 degrees farenheight. I know that I have been through some that felt every bit that much swimming, but that's kinda hard to guage.
The point is, fish are more temperature resistant than you think, particuraly the natives.