Here's a quick how-to on reprinting your own cartridge labels to make a game in crusty condition look pretty good.
You'll need to know the exact size for the labels you want. I'll start a table here and add to it as I measure them out. All sizes are in mm, listed width * height.
Gameboy & GBC: 42 * 37
Gameboy Advance: 43.5 * 22
N64: 54 * 62
Atari 2600 main face label:
Atari 2600 end label:
Atari 2600 Activision:
Search on the internet for an image of the label you want. Try to find one that is oriented well and is decent resolution. It can be just of the label or of the whole cart. We'll crop it in step 3. "Copy" the image to the clipboard.
Now use the image editing software of your choice to crop the image, rotate it slightly if necessary, etc. We want to get just the label. I use a free program called "paint.net" (PC). Once you get it just right, "copy" this image to the clipboard.
Critical: Printing things to exact sizes on modern computers is hard, so this is the step that trips most people up. The secret is to find a program that does layouts or PDF's, as those are always done in precise sizes.
I use a free program called "Inkscape" (available for PC, Linux, Mac).
Open a new page and "Paste" your image in this program, and then size it using the table in step 1. Move it to the upper corner of the page. Optional: copy/paste that resized version and move it over a bit. The goal is to have two copies printed out so that if you screw one up, you have another ready to go. Optional 2: If you are printing on fancy label paper, you may want to resize the page first.
Print it out! I am not a perfectionist. I just want things to look decent. I use plain copy paper on an inkjet printer. Use whatever you want on this step.
Optional: If you want to give your label a gloss finish, you can slap a piece of packing tape over your printed labels. Do this before you cut them out. I usually don't, but it does look nicer if you do this.
Carefully cut out your reprinted label. It is important to cut right along the edge with no white paper showing. Take your time. Use a magnifier to make it easier.
Glue it on! For this, I use a simple Elmer's glue stick. The nice thing here is that it isn't permanent. If I don't like it later, I can easily peel it off with no damage to the cart or even a label underneath. Take your time, keep your fingers clean, use a magnifier, and it will turn out nice.
BOOM! Done.
Some examples:
BEFORE images of two working GBC carts with well-loved labels:
Here's where to type in the label size in Inkscape:
What my print out looks like:
And finally, the finished product. Note that for Flintstones, I cut my reprint way down to have just Fred. I figured the original label was in nice condition except for that wear spot in the middle.