Never trust a website that endorses acne cream as a 'presevation' method.
We know it's horribly detrimental to ponies, proven to cause irreversible, long term damage. And cling wrap? Oh heck no. That's one of the worst materials you can put next to anything. One of my AMS professors had us wrapping pencils in cling wrap and leaving them somewhere warm for a week, after which the paint literally falls off the pencil. It was horrifying. There's always an inherent risk to doing restoration or conservation, but it's something that should be warned about clearly up front.
That said, nothing's impossible when dealing with plastics, because 'plastic' isn't one material. It's hundreds of thousands of different composite recipes with wildly differing properties, and what works on one given blend may not work on another. But I'm not inclined to believe one person says aluminum foil yellowed a pony without any sources, proof, or knowing what other variables may have been involved, when many others have used it and not experienced any problems. That strongly suggests there's something else going on. Commonality doesn't always equate to causation.
If you can see light through a material, it's not going to block UV. Paper towels are not effective. It needs to be opaque.