Method validation(vendor change)

If vendor is change at that time is it required to validate method of finished product ?

If new API having 2 more impurities then existing one, so in that case only raw material method is to be validate or we have to validate both FP AND RAW ?

At the same time we are performing the process validation(time of vendor change) and upto my knowledge method validation is the part of process validation so can u guide about what are the different factor affect at the time of vendor change regarding method validation ?

Actaully we need to validate both RM and FP