It's a good idea to turn the contrast down anyway.
With all due respect to those who prefer the breakin period with slides, I do not see the benefit with regard to aging phosphors evenly (although if there is a reference I am more than happy to learn). That said, I do believe that any electronics we buy are going to fail within the first few days or be reliable for a much longer period, and constantly running the set (whether slides or tv/cable broadcast) is a good idea. So what the heck - run the slides and 'presume' that the placebo effect kicks in. Regardless, you'll benefit.