You can switch to 10w40. It'll actually prolong the life of the engine as 20w50 is too thick a grade for winter use in our country. The greatest wear and tear happens to your engine at startup when there is no oil. If you're using 20w50 oil in winters then it'll take longer to start the engine and for the oil to warm up and reach all the parts of the engine. The oil pump will also have to work harder which can cause it to fail prematurely. In our environment, 10w40 is the best oil for year round as it is good for temps as low as - 20C, so there will be no problem starting the car in winters, and it can also provide adequate protection in summers.
