That works to a point (I do it lots), but unfortunatly parts quality varies so you need to be aware of what the xml should look like (which comes with experience in parts making) to be able to evaluate whether the part you are copying is going to work. I often mix and match bits and pieces from various other parts to get where I want to go (and steal good artwork in breadboard since I'm no kind of artist). If breadboard is working I'd keep it and just change pcb if that's all that's breaking. If you upload the final result I or one of the others of us will have a look and point out errors. Its in all our best interest to encourage people to make more parts Image may be NSFW.
Clik here to view. At some point (which unfortunatly isn't yet) we need to do an audit and correct on the core parts distribution to correct the existing errors (the grove parts for instance all seem to use the path for pads which doesn't work). I'm slowly working on a python script to check and correct for Fritzing which objects to some of the things such as CSS style xml that Inkscape does, but again I'm not entirely there yet. That script will complain about connectors that aren't in one of the known working geometries (I having been bitten by paths before Image may be NSFW.
Clik here to view. ).
Peter