I wanted to change the backlight LEDs from amber to blue, red or white. Red would be good so as not to mess up your night vision. But I didn't have any LEDs that would work at the drive voltage being supplied. :( By this point I had documented how to take the device apart, so I thought I might as well put it up here.
If you are planning on changing the backlight, you will need two 3mm round (or flat / smd) LEDs that will shine brightly at 1.95V.
Taking the etrex apart and putting it back together again was surprisingly easy, but a little painstaking. Looking at mine now, you can't tell it's been apart.