directory-content-symlinker is a Windows command line tool that will search two directories (the target and the destination) for duplicate files. For each duplicate file found, a symbolic link will be created in the destination directory pointing to the file in the target directory. The file in the destination directory will be removed (sent to the Recycle Bin).
C:\symlinker -t "C:\keep-these" -d "C:\replace-these-with-symlinks" -s "*.txt|*.doc"
-h, --help Show this message and exit.
-t, --target=PATH The PATH to the files symlinks will refer to.
-d, --destination=PATH The PATH to the files symlinks will be created for.
-s, --searchPattern=VALUE Pipe (|) delimited list of search patterns used to
find files. Each pattern is passed directly to
Directory.GetFiles so see docs for that.
This program uses the mklink command line tool to create symbolic links and will therefore probably have to be run as Administrator.