Need help altering a dialog box

I've been making MuseScore more banjo-friendly, making it deal with the weird 5th string properly. I'm mostly done, but there should be an extension to the "edit string data" dialog box, adding a column to allow a single string to be capo-ed independent of the others. I've been toying with QtCreator, but the whole thing has me flummoxed. Is there any guidance anywhere about how to do this? Anybody willing to be my guru?