Sometimes, when fumbling with your keys, you spend a lot of time staring at them to figure out which one you need. If you can identify them by touch, however, you don't have that problem. With a little Sugru, you can easily add those variant textures.
As you can see in the picture above, a little bit of spotted Sugru creates a nice bubbly texture. You could also use straight or wavy lines, larger bumps, and a variety of other patterns for other keys. As well, because Sugru comes in various colours, you can make your keys easier to differentiate when looking at them.
For more Sugru key hacks (including a cool LEGO option), check out the full post on the Sugru blog.
11 ways to sugruify your keys [Sugru Blog]