It depends on the specific fixture.

But then, the problem is, it depends on the specific fixture. They aren't exactly putting "EASY TO REPLACE LEDS" on the box. I can't climb up to the store display model and start hacking away at it to see if I can get to the LEDs, replace them, and reassemble it correctly.

What I saw last time I was in a store where the fixtures were on eye level looked like a lot of glue, one-way tabs, and LED strips of unknown and custom provenance were being used. I'm not really looking for this sort of experience in a lighting fixture. YMMV and more power to you.