I just tried this today, and if you guys are interested I'll write a tutorial on how I did it...
So, I love dark jeans, especially on my little boys, but I've found that after several washes they fade... a lot. It drives me crazy. Well, I've wondered for a while if I could dye them dark again, or if that would ruin them. I finally broke down and tried it on the only pair of jeans Bug has... and it turned out great! They look almost new again! I still need to find that perfect shade of dark denim dye, but for now the Rit Dye in navy is doing the trick.
So if you'd like me to show you how I did it, let me know... it is super simple, but I know I was scared going in blind. :)
Have a good one!!!