Sure there is a sound solution: dig in to the source which the developers have provided and make the necessary changes. It just isn't easy or effortless. In this case that probably isn't necessary since all that is really needed is to convince Fritzing that your part should be considered part of the family of core resistors which is possible by changing the part meta data (it may require the color bands or at least their labels as the core scripts change the color bands and may be unhappy if the labels aren't there). As far as I am aware the developers don't read the forums, they have not been seen to comment even if they are reading them. For instance offers do translations to other languages (which is far more valuable than enhancement requests) have gone unanswered for months. When I finish the current part I'm working on I'll have a look at this.
Peter