I doubt you will be allowed to rebook now for flights in April. Hopefully the airspace closure will be over by April. If not, LX should take care of you and make the rebooking if you arrive late at ZRH and miss the UA flight. Forget about getting rebooked in advance. The issue is here that you are on UA award and LX will be reluctant to touch it even if you misconnect. You may face agents trying to convince you to contact UA as UA issued the UA ticket. However, I believe that there is a good chance that LX at ZRH airport will rebook you without fuzz. Forget about calling LX to rebook; call center agents can't/will not touch award tickets issued by other carriers.
If you call UA to rebook now, I class needs to be available for the new flights and you will have to pay change fee - it will be considered a voluntary change of the award ticket and treated in the same way.
Last edited by SK AAR; Mar 17, 2019 at 6:59 am