If you change from 316L grade to 304 Grade of Stainless steel, you may change your filler wire / electrode from E 316L to E308/E308L type to match the parent metal chemical properties and reduce cost of filler wire. As far as ASME SEC-IX is concerned, neither the P no, F no. nor A no. is being changed and so requalification is not required.However AWS classification of the filler is a supplimentary essential variable ( when the material requires impact properties ) and when the filler is being used as a corrosion resistance alloy.