Installing fat bike tires on a BSO for winter riding(condition of averaging -23 C for 2*17km). Is it doable, safe?
Fat bike tyres (3.8" or bigger) are unlikely to fit in the frame or fork of your BSO.  In addition, such large tyres require wider rims (typically 50-100mm internal width) which you are also unlikely to have.  Finally, fat tyres have their advantage in 'floating' over sand or snow, however they won't grip on ice as well as a studded tyre.