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Hi, I'm Mike G and I'll be assisting you. You'll need to check the model number on the inside of the can. Any notation of "IC" indicates that insulation may be in direct contact with the exterior of the can. If not marked the insulation needs to be 3 inches away to prevent a fire hazard. That type of can would need and enclosure over the top of it keeping the insulation at the 3 inches.
Never saw one that could be. Do you have access to a crawl space above them?
If not IC rated, drop the interior of the fixture and stuff insulation at least 3" away of if rated stuff as much as possible. There isn't anything else to do but replace them. If they were installed as new work, there is a frame that would interfere with installing a new can from below.
Very good. You're welcome.