That is generally the recommended way to make new parts. It is possible if you are familiar enough with parts editing to make one from scratch but you generally (or at least I do 
) need to run it through parts editor to get it properly registered with Fritzting afterwards anyway. If you upload the fzpz file after you have added your images (even if it shows as a red screen in fritzing) one of us can probably wrangle the connectors in such a way that you can see your images in fritzing to do what you need, the connectors being incorrect are what is blocking frtizing from showing your new images. With all of the files I can (and usually do) use a text editor for the fpz file and Inkscape for the svgs to get it to a state that Fritzing will load.
Peter.