The "growth habit" of Weeping moss is long, overhanging shoots. Usually with quite short branching on the long shoots. This will create a downwords, or hanging, appearance if the moss is placed freely on a piece of wood - or otherwise, having space under it. The newest growth of long shoots will be lighter green colour, giving the "tear-drop" effect, that it is named fore.
- so in a way, you could say that trimming he moss will actually work against it hanging ( trimming, ofcourse, has to be done at some point, to avoid the moss suffocating it's lower parts from lack of light and flow).