i have that plant and yes once it reaches the top just trim it about a 1/3rd of the way down, if you want a more bushy looking plant trim it 2/3 to 3/4 of the way down and it will sprout 2 or even 3 more stems, thus making the plant look more fuller and bushier i am trying to do this right now with my plants,
just cut the stems at a 45o angle and it should be fine here is a picture of my latest trimming
as u can see i cut it close to the substrate about 2 to 3" above at an angle with VERY sharp pair of scissors sharper the better, blunt scissors or just snapping it off will crush the plant you need a clean cut. check over to my journal (Green Phantom) in my sig for update pics as i post them on later this week
EDIT: oh and i forgot to mention, the part you cut off you don't haft to throw that away just push the stem into your substrate and it will sprout roots in the next few days and grow like a new plant thats how we propagate stem plants just like the picture above u can see that part that still in the substrate is growing roots above substrate your new trimmings will do that
good luck and enjoy, ps the only part that is likely to die if the part you leave behind the part you cut away will survive as it has majority of the leafs on so planting them back in and if your old part does die then there is no loss