I unfortunately had a notebook have a syntax error and I would have lost weeks of work. To fix this, I was able to save my old notebook as a .rtf file without any excessive data loss. When I convert this .rtf to .nb by saving the file as .nb, Mathematica is able to open the notebook almost as I left it. The problem is that this results in the loss of all special characters, which I have many of. Is there any way to maintain the special characters while creating the new .nb?
StringReplace
could do that if you can import the file content as string. If the special characters were just ignored when the file was exported, then there is probably no alternative to going through then file manually... $\endgroup$