After it got pointed out to me that in LTspice it was possible to tag resistor values with the 'noiseless' keyword, I reckoned it should also be possible to specify the temperature of a resistor. Indeed, it is possible to assign a value of '50 Temp=-196' to a resistor and to get the correct thermal noise contribution for that resistor in the noise analysis.
I couldn't find any mention of it in the manual, but this is very useful to me.
Jeroen Belleman