No, it doesn't matter. The volume in the tire is virually the same, therefore the pressure does not change. There is a minor increase / decrease, but nothing that you would notice. You will have a greater increase in pressure from building up heat in the tire, that is why it states a "cold" psi rating.
I autocross occassionaly and we will build 2-4 lbs of pressure in a 60 second run in tires just from the heat buildup. So the miniscule amount of pressure difference loaded vs. unloaded won't impact the overall performance of the tire.
