This appears to be a simple foreshortening effect, making the multiple beams emitted from the Star Killer Base appear to be a single beam until it entered the Hosnian system of planets when in reality, it was always a set of half a dozen separate beams traveling along much the same path.
This is backed up by the film's official novelisation which makes no mention of the beam splitting along its path, let alone at the command of Kylo Ren.
Penetrating to within a predetermined distance of the containment field, an immense hollow cylinder permitted a way out while ensuring that when the weapon was unleashed, gigantic groundquakes would not roil the world’s fragile surface.
When the weapons engineers fired the device, a breach was induced in the containment field. At incredible velocity and accelerating exponentially, the concentrated volume of quintessence escaped, transforming as it did so into a state known as phantom energy and following the artificial line of egress that had been provided. Assuming that the rotation and inclination of the planet had been taken into account, the released blast of concentrated phantom energy would travel along a perfectly linear path, punching a small Big Rip through hyperspace itself until it left the galaxy