The $5.00 fee is for both downgrades and sidegrades and switching premiums is considered a sidegrade.
The only time this fee is sometimes waved is when they offer some sort of special like HBO and the Starz pack for free for 3 months and you cancel just before the 3 months are up or the Cinemax for a penny for a year and you cancel that just before they start to charge you. This was my understanding anyway.
I switched from Cinemax to Showtime about 3 to 4 months ago with no fee for the change. I have HBO also. So, I essentially went from one bundle to another. I'm a long time customer under no special promotions.