It depends on the manufacturer. I have one I got from an office supply store; that one I can replace the bulbs in. I have another, I believe it came from Ikea, can't replace that one.
There is a LED bulb in my Brother 270D, it went very dim. Couldn't figure out how to replace it, so I took it to the authorized technician and was told that machine is considered "disposable". In other words, you can't replace the bulb, they assume you'll just replace the entire machine.
Very aggravating, especially since the machine works fine!