The FLAC project has metaflac. LAME should have a metalame application modeled closely after metaflac. There are a handful of similar apps that have been created over the years, but they're poorly maintained and almost all of them are buggy or incomplete, missing things like the ability to add TXXX tags or something similar.
Like metaflac, the ability to compute album level ReplayGain should be included. The ability to use Windows wildcards to specify an Mp3 input file list on the command line would be helpful. That's one thing that metaflac does not do when run on Windows.
All of the functional pieces for reading and writing metadata from Mp3 files should already be present in lame itself. The album ReplayGain capability and perhaps some added command line parsing would be new.