It is easy to convert a symlink into a hardlink with ln -f (example)
It would also be easy to convert a hardlink (filenames link and original) back to a symbolic link to link->original in the case where you know both files and define yourself which one is the "original file". You could easily create a simple script convert-known-hardlink-to-symlink that would result in something like:
convert-known-hardlink-to-symlink link original
$ ls -li
3802465 lrwxrwxrwx 1 14 Dec 6 09:52 link -> original
3802269 -rw-rw-r-- 1 0 Dec 6 09:52 original
But it would be really useful if you had a script where you could define a working directory (default ./) and a search-directory where to search (default /) for files with the same inode and then convert all those hard-links to symbolic-links.
The result would be that in the defined working directory all files that are hard-links are replaced with symbolic-links to the first found file with the same inode instead.
A start would be find . -type f -links +1 -printf "%i: %p (%n)\n"
Best Answer
I created a script that will do this. The script converts all hard-links it finds in a source directory (first argument) that are the same as in the working directory (optional second argument) into symbolic links:
https://gist.github.com/rubo77/7a9a83695a28412abbcd
It has an option -n for a dry-run, that doesn't do anything but shows what would be done.
Main part:
The -links +1 --> Will find all files that have MORE than 1 link. Hardlinked files have a link count of at least two.