Yes but it may not be suitable for high frequency or high power. Intrinsic loss due to hysteresis is large for soft iron because of residual magnetism. If you are planning to use for low power and low frequency perhaps you can use it safely. If it is already has an oxide layer on the surface, then using a varnish in addition is going to reduce some audio noise. If it is having a zinc or tin plating then it will get too hot even at 50-100 Hz (depending on the power handling).