well first once removed you MUST recalibrate them, since you have a 99 up its not that difficult. If you find you MUST remove them you can use two pieces of bent metal/plastic to slide under each side of the needle base and push down to pop them off both sides at the same pressure, a slight angle is needed in the item so once its flat on the gauge face you have something to push downward to slide the needle up and off. There is a VERY thin piece of metal holding in the needle so do NOT break it. Once off to put them back on you just slide them back on the metal rod (very thin). Dont push them down all the way, see how far they are now and put them back to there (remember the gauge cover over the stock gauges adds depth so take that into account).
The speedo and rpm gauge you can use your diagnostic to reset. Drive down the road and stick them back on using the diagnostic readout as a guide
not fun but not bad with a helper to steer the car while you mess with the needle. Test at 55/45/etc make sure its right. Same with RPM.
Battery/Temp/all but gas see where they are under normal operating (fully warm engine) and put them back there when the car is fully warm/normal operating temps.
Gas... fill up 100% see where needle is and put it back there. Or just see where its at and put it back there before you drive any more~ car has to be cranked for all of this though.
Snug them on and once you pull over/stop you can set the needle to the right height off the gauge face.
I wish there was an easier way but thats it