Changing png to jpeg help needed

I have 23 png files at approx 700x525px, and they are in a fla timeline. After I initially imported the files into the library, I set the properties to png for best quality reasons. When they were placed on stage and subsequently brought into the timeline they were converted to movieclip symbols to apply various attributes such as alpha and brightness parameters and some blending modes, Also some (quite a bit) of tweening has been applied. I need to lower the overall bandwidth (re: size of the published Swf) and I am wondering if I change the properties in the library of the orginal png bitmap images to jpeg 60% quality, it this procedure will dynamically update the movieclip symbols previously created, or not. In which case I might need to rebulild quite a bit of stuff? Anyone have any insight on this, suggestions, experience, etc…

thanks