For sure the OP can change the destination. The real Q is how much it will cost to do it. Most likely the fare for the return segments of the ticket will have to be recalculated; the OP may not like the additional amount that will have to be paid to have the return segments changed. But give it a try.
Another option is to wait it out in Mexico/until it is possible to enter Norway again. Mexico is not the worst place to spend time when most other parts of the world are in lockdown/qurantine (apparently social media influencers, celebrities, sport stars etc are of the same opinion flocking to Tulum at the moment).