It's not a problem provided you have enough wire. If you have to lengthen wire, don't use crimps, solder the extra wire length and use shrink tube to insulate. (the reason for this is solder conducts more current than does crimps)
Make sure that your speedometer cable doesn't have too steep of a curve otherwise you're speedo needle will bounce.
This would also be a good time to force some light greese into the cable housing.
If you want to greese it correctly, remove the cotter key securing the cable located on the front left wheel bearing dust cover and remove the inner flex cable from the speedo end. Coat the inner cable using light greese and then re-insert it into the cable housing.
Before removing wires from the gauges, provide youself with a good diagram of their original locations.
One of the easiest ways to mark wire location is to numerically mark the wire location on the back of the gauge with a Sharpie pen, then, attach a small piece of tape to the wire. Using the Sharpie, write the corresponding number onto the tape attached to the wire.
In other words, wire #1 ataches to #1 spade connector on the gauge and so on. This makes it very easy when re-assembling the wires and also for future removal.