There has been a few minor changes in UTMB mandatory kit list. Like often with the French, the regulations can seem a bit confusing at times for us foreigners, due to different language and culture.
For example, why the roll of adhesive elastic tape has to be 6 cm wide, but only 1 meter long - wouldn't the standard 5 cm wide and 3-5 meter long do as well, if not better? How can you keep your phone switched on for two days, if the battery lasts only one day? And do you really need a 'tri-band' phone to be able to use it in all three countries involved (France, Italy, Switzerland) - I don't think so.
They demand long trousers, but then hasten to add that 'a combination of leggings and long socks, which cover the legs completely' is ok - so probably any clothing that covers your legs (like over-the-knees tights and calf sleeves and running socks) would be perfectly acceptable?
In any case, you are still required to carry a waterproof jacket with a hood, waterproof trousers, waterproof gloves, and a warm hat at all times, in addition to your normal running gear.
The main thing is to get the best equipment possible for you. Test it in bad rainy weather well before the race. In the mountains you better be safe than sorry.