Making my own custom toys has never really appealed to me due to my lack of talent and money for all the times I’m sure to screw up. However, a very simple an inexpensive modding without a whole lot of effort.
Reprolables.com makes custom stickers for a few different types of toys, most notably for Transformers. Just add some stickers to certain Transformer figures and you’ve got a different look. Check out this Wheel Jack:

That’s some great G1 goodness. A lot of the other stickers make figures that I wouldn’t have thought about getting before almost worth it. There’s lots of other goodies there as well like customized license plates, an evil Jet Fire color scheme, and different faction stickers including a Cobra symbol.
Okay, I think I’m done geeking out for now.
Transformers, toy collecting, Hasbro