This would be a terrible idea:

• The crews are not trained on the MG42 and they definitively would not have had the possible many years of muscle memory build crewing the M1919
• Adding foreign weapons to squads on the assault would complicate resupply logistics to the detriment of the speed of the assault
• Most importantly, firing a very recognizably sounding MG like the MG42 would turn you into a magnet for friendly fire, including mortars and tank rounds.