That depends on what you mean by trimming below the screen. You absolutely don't want to remove any leaves that are in the light at the top of the canopy, but after the flip, if you see any smaller branches and leaves that are UNDER the canopy and they don't get any light, AND they don't look like they will make it up to the light, then you can remove them. I only remove a couple of the lower branches every few days so that I don't stress the plant with large amounts off cutting and removal. If you have "spindly" lower branches that have little or no chance off getting above the canopy, then cut them all the way back to the larger stem or main trunk. What I mean by "the larger stem" is some of the branches will go out from down low and will extend several smaller branches up through the canopy but will also have 2-3 smaller branches that are well below the canopy with little or no chance of penetrating the canopy to become new bud sites. These little off-shoot branches can be removed while leaving the bigger branch that does penetrate the canopy.
As they flower you will see little "sucker buds" develop around the base off the trunk and on the lower branches in places below the canopy. You can remove these as well because they do nothing but suck up energy from the plant while never becoming viable, mature, ripe buds. Removing these a few at a time will allow the plant to send that energy to the tops, and because the plant is in flower, it will largely ignore the loss of those buds. They call them "sucker buds" because they suck up energy from the plant, they and sucker you into thinking that they will be worth keeping, but they aren't.