String Trimmers

I recently bought a factory reconditioned Husqvarna 224L string trimmer from Amazon, which shipped out of Northern Tool. This is a 4-stroke unit. So far, so good, other than the unit shipped with almost no string. I am also in the market for a 4-stroke leaf blower because I don't have much luck with 2-cycle engines. The saleman at the power equipment place I visited cautioned me against a 4-stroke blower, saying that holding it in any orientation other than horizontal to the ground could cause oil to flow into the cylinders and damage the engine. Thinking of how this might relate to my 224L trimmer, this worried me, because I planned to use the 224L to cut a nice edge to my beds by holding it such that the string rotated perpendicular to the ground, as I have seen many professional lawn services do with their trimmers, which are probably 2-cycle. Do I need to insure that I only hold the 224L with the head essentially parallel to the ground (slightly angled per illustrations in the manual)? The subject of vertical edging is not addressed in the manual. I don't want to damage the engine, but holding the unit such that the string rotates perpendicular to the ground is about the only way to get a sharp edge with Centipede grass, which spreads horizontally.