I tried Peacecup's method of using a paint can opener to remove the dispersion screen and just bent the heck out of the opener.
"New" Ponte Vecchio Lusso spitting chrome particles

I want to remove the screen to see why water only flows from the front half of the screen, (it didn't used to do that). I suspect those little rocks, like the ones you find in your faucet screen, are blocking the water flow.

Is there another way to remove the screen without disassembling the group?

You have to find the sweet spot with the dispersion screens. Try a largish flat head screwdriver and pry it around the gaps where the portafilter lugs would normally enter. They do pry off eventually.