Yes they could but this will just destroy Swiss economy and likely create out of control inflation. Doing this is always a risky policy. SNB has told many time

Yes they could but this will just destroy Swiss economy and likely create out of control inflation. Doing this is always a risky policy. SNB has told many time that they will use unlimited means to keep the value of the Swiss francs however in 2015 they had to give up on the promise to keep a 1/1.2 EUR/CHF exchange rate. What history told us is that even hedge fund (like Soros in 1992) can bring a central bank to its knees.