you only need to drop the voltage, when you drop the voltage the current will also drop.
you will need to make it so the voltage is adjustable from 6.3volts down to around 4.0 volts.
again i made the same type of variable power supply when i was working at hawko. the leds that are in there bud lighting works on 12volts with 1 led, or 2 leds in each fitting wired in series.
the led pcb would then plug in to a wedge socket, the wedge sockets were wired in parallel. The reason why they ran on 12 volts is because of the cable lengths.
any way some customers where complaining that the leds where to bright in some applications so I designed a regulated power supply with a trimpot (that controlled the voltage regulator) to dim the leds.
In saying that some led power supplies regulate the current as they are made to run x amount of leds as fire power suggested.
I still have a schematic diagram for the variable led power supply.
the led pcb for the wedge socket is pictured below, the pin configuration on the sockets used for these leds where different than the pinball 555 sockets, if you plug the pcb in the picture below onto a pinball socket it will just short the socket out. (the one pictured had a couple of wires soldered on to it at one stage, hence the untidy solder at the bottom)
