69 Barracuda Side Markers

I need to replace the side markers on my 69 Barracuda to re-register my car. I've done a lot of engine and drivetrain work on my car, but not too much on the body. Are these easy to replace? I got some replacements from Layson's, but they didn't come with any instructions. From the look of the replacements, they should just snap into the holders. Are there any tricks to make this easier? I re-painted my car about 6 months ago and don't want to mess up the paint job.
Thanks for your help.