How much patience do you have? It's possible, but you are going to need a ton of patience and time.

If you go at them with a heat gun and no oven, rest assured you will mangle the housing and or ruin them in the process.

I would bake them at 210 degrees for about 30 minutes or so just to get the housing warm, wear gloves, and take them out of the oven. Take a utility knife and cut the sealant between the channel and the lens, go around the whole lens. If you can take a small pick or something to get under the lens to the sealant on the bottom side of the channel (part of the black housing that the lens rests in), and pry a little bit, you may be able to get it in an opening.

You most likely will need to heat up the housing with several baking sessions at low heat but you probably can get them open. I don't have the patience for it however.

You can cut them open with a dremel but you will need a damn good adhesive for re-sealing everything.

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