Anytime you change something about a load (primer, brass, seating depth or powder lot number) you should reduce the powder charge by about 3-5 grains and work back up to your original load while watching for high pressure signs.
That said......Seating the bullet deeper in the case shouldn't increase pressure by much until you start compressing the powder in the case. A change in case volume due to bullet seating depth doesn't have as much to do with pressure as most people think because the brass is still going to expand against the walls of the chamber, and the chamber is still the same size. When you change the seating depth, you're actually moving the pressure curve. Seating the bullet farther into the case gives the bullet more of a jump to the lands, and allows the pressure in the chamber to build more gradually instead of a sudden spike when the bullet hits the rifleing too soon. Conversley, if you seat the bullet out to kiss the lands (and are loading a hot load) the bullet doesn't have any "free bore" to jump across, and therefore the pressure spikes almost immediately. This can cause signs of high pressure (flattened primers, cratered primers etc, etc).
