For imported data, how do I change the two Random Variability components?

The Random Variability values (and the mean daily profiles) are inputs when you synthesize load data from mean daily profiles, but they are outputs when you import time series data.  If you import time series data, HOMER will calculate all those values, and if you then switch to enter daily profiles, they will all stay at the same values and become editable.  So you can change whatever you want to change.