For the most part, emblem removal is more knowing how it's attached rather than special tools for removal.
Some emblems are attached with "bullet" grippers, others with stamped metal nuts, others with sheet metal grippers.
Fast explanation on these types.
Bullet grippers are difficult to explain, but if you can imagine this you'll have the idea. Imagine a beer can that has had both the top and bottom removed, then the sides of the can have been cut in such a way as to expand parts of the sides outwards. Additionally, the turned metal rim of the can has been turned outward to form a flange, lastly split the can down the seam of the can.
The stem of the emblem fits inside the can, and the outsides of the can press against and underneath the sheet metal, with the flange resting against the top of the sheet metal.
These connectors are usually used on sheet metal where you cannot access the back side at all, or it is very difficult to do so. To remove an emblem with this type of connector, you usually slowly and carefully pry up the emblem working your way on all the connectors. It isn't unusual for the bullet gripper to come up with the stem. Unfortuneatly this type of connector will usually grip the paint both on the way in and out and it is very difficult to impossible to remove without some paint damage.
The stamped metal nuts are just that, nuts made from stamped metal, that have a thread that bites into the stem of the emblem. This type of connector will for the most part be accessible from the back, or at least the side in order to be able to put a wrench on it. This one rarely causes damage to the paint either on installation or removal, unless the emblem was overtightened or it was jarred.
The sheet metal gripper is a flat piece of sheet metal with a hole in the center and a couple flanges that bite into the stem once inserted. Usually very easy to install, but tricky to remove without damaging or breaking the stem if you're not familiar with them. These also are usually accessible from behind since they must be pressed onto the stem. To remove these, you usually pull up one or both of the flanges that are biting into the stem and wiggle it back and forth until it's off.
There are other methods of attachment, but these are the three most common used on the Z's.
The most important thing in order to NOT scratch paint is to BE PATIENT. First examine the emblem and see if you can get to the back side. If you can, check this side out BEFORE you begin to pry etc, as that will tell you the type of connector you're going to find.
Replacing emblems without damaging the paint is definetly possible. For 72 240z the hood, c-pillar, and side emblems use the bullet connector. Simply pry the emblem up and off using a plastic blade (slowly and carefully). I don't know about the deck lid emblems.
Its the hood emblem I'm looking to remove. I don't mind if there is a little paint damage on the holes underneath the emblem, as long as the chip does not occur outside the edge of the emblem. I will just touch up any damage underneath to prevent any rusting.
When you put the emblem back on, make sure you put some double sided tape underneath for safety, because the bullets are never as tight as when they came out because youve worn them. 20 year old plastic can be fairly brittle.