OK, I found a solution to the problem. First set the default disk temperature warning values to what you want it to be for SSD drives (I use 70C and 90C). Next go to each individual non-SSD drive from the main menu and override the default temperature setting to a value suitable for a HDD drive (I use 48C and 55C). In this manner, the SSD drives have the default value for disk temperature warnings while the HDD drives have a different, custom value.
Maybe you are not allowed to override the default value with a higher value
Should this issue be marked resolved? I can't find how to do that