Short shifters will not harm the internals of the transmission as long as you engage the gears properly. People with older Z32's found that when they upgraded to short throw shifters, that if they shifted faster, then they could potentially grind a gear when up shifting/down shifting.
Installing a short throw shifter is very straight forward and can be reverted back to stock at any point in time. On a 370Z in particular, you really only need a 10mm socket, 12mm socket, a ratchet, about a 3" extension and a little bit of patience. Aside from these basic hand tools, a good set of ramps is also needed. To unbolt the shifter from the linkage on the transmission, you must do so under the car. There is plenty of room in the transmission tunnel once you get under there. The reason you cannot access this 12mm bolt from the top is that the cut out in the trans tunnel is too small to fit your hands around the linkage.
I just got done installing the AMS Adjustable Short Throw that we offer onto our Project 370Z here in the shop. From start to finish it took me about about 30 minutes. The biggest pain for the entire project would be unscrewing the factory shifter, but we . These things are a pain to remove, but can be done so without damaging the shifter itself, again you will have to exercise patience.
The AMS Adjustable Short Throw that we have installed on our car can be found here on our website:
AMS 370Z Adjustable Short Throw Shifter