As I said in the comments, I believe my findings deserve an answer on their own. These matters are urgent and I'm a little troubled by what I've found.
I've sent emails to three major rope manufacturers (Petzl, Beal, Mammut). Only Mammut cared to even write me an answer - which made me feel lonely and friendless. But anyway, I don't think there would be any major difference between all answers I would receive.
Remember I asked for clarification about topics that are not contained in either EN 892 or the UIAA standard.
Regarding UV Exposure
Mammut clarified this point in a way that makes sense to me. We should not be worried about UV damage to the rope because the sheath, which is approximately 1mm thick, breaks the UV before it hits the core. This is true for all modern ropes, and some of them actually exaggerate: Sterling's Marathon Pro has a double sheath, which I believe makes this rope's half-life sort of infinite.
Regarding Temperature Range
Mammut says warm temperatures are not a major concern and that they have tested this internally. At this point I sent another email saying that testing stuff internally doesn't convince me unless some statistics are shown to me. Mammut said that they couldn't sent me any statistics, and that they tested the ropes both for the standard temperature (23ºC) and an extreme temperature (50ºC). They say the outcome was the same. I don't believe it. I think there are significant changes in elasticity - but I do believe it's not dangerous to climb in the heat, it only wears your rope significantly more and might turn the catch stiffer if you regularly take whippers in the heat (my opinion).
Regarding low temperatures, my hint was correct: it might not be safe to climb in extremely low temperatures. According to Mammut, cold temperatures might shrink the rope in up to 10% of its length - this makes the catch stiffer. I don't think it would be stiff enough to hurt someone or to break the rope, but I do think taking a factor 2 fall on a frozen rope is not at all a good idea. A major problem about climbing in low temperatures has to to with the heat generated in the impact melting the ice and the rope becoming wet.
Regarding Wet Ropes
This is where the problem is real. According to Mammut, I should not be worried about my rope unless it is wet. Some home-made studies address both the problem of water and dirt on ropes. I also remember having read (I won't look for this reference right now, but I think it was UIAA itself) that climbing ropes might lose up to 80% of their resistances if wet. The combination of water and dirt might be specially dangerous. Mammut said that they have a very strict method for building dry ropes because water is so dangerous - and that sort of makes me wonder why the hell people still build ropes with non-dry treatment.
Conclusion: don't worry about the UV, and unless you're climbing in an icy environment with a non-dry rope, don't worry too much about low temperatures - but keep in mind your rope might be much shorter. Don't take factor 2 whippers (ever, if possible), since in extreme cold they might really hurt or break you up. High temperatures are not dangerous, but your rope will wear out faster climbing in them. Also, high temperatures might come together with high humidity, which is the only thing you should be really worried about.
Curiosity of the day: manufacturers like Mammut do take a seat in the meetings that decide changes in norms and standards. This means they can do something about what's missing in them, if they want. I'm inclined to say that if they are not insisting on including these things in the norms, it's a little because they don't matter much and a little because no one wants to spend more money doing more tests - even if they would clarify a lot.