RTNG is the semi-official ID3v2 field for the song rating. firefly reads it, and popularimeter iirc.
What you needed to have is a program (preferably console based) that writes id3v2 tags to a file specified.
When I still had my slug I couldn’t find anything, maybe on my new NAS with full-blown debian there are some tools. I haven’t looked for any yet, tbh.
As far as the remote is concerned: Not all remote codes are being picked up by the SoundBridges.