I'm not sure about support for this within Lily/Frescobaldi, but I know a similar mechanism exists in Lyx. At the least, you can issue commands to a parent document from within the editing environment for the child document. Not sure how useful it would be, but LaTeX has a package (srcltx, here:
http://ctan.org/pkg/srcltx) that embeds a markup into child documents (in this case the DVI output) that links back to the generating TeX file. But that sort of thing would have to involve a tag or markup or something in the related child documents. Someone who knows much better how Lily/Frescobaldi handle child documents would have to answer that.