Sometimes I do some tidying of my files, this doesn't affect me when on changing tags as I can reload the data and it is taken by Mixxx but sometimes I also might change actual filenames. This causes the file to get relisted as a new entry with no BPM, Key or Cue Point information and the old copies shown in Missing Tracks. Sometimes it might also be attaining a higher quality or new version/mixdown of a tune with a slightly different name.
I would like an option to be able to (right) click on a single file within the Missing Tracks window and select Relocate Track, which would take you to a library view where you can search for the track (maybe first showing a handful of files that have some similar names/components saying search for Artist and Title and show the top few matches before giving an option to open the full library to search manually.) One you have located the track you can (right) click it and copy all the relevant information to it, then load it and check the cues etc are actually in the correct positions (in case the file is actually different.)
It might also just generally be useful for have a right click -> metadata -> copy/paste all. Very useful for moved tracks, but potentially also useful for songs with variations (e.g. VIPs, club mixes, extended versions, or remixes within the same genre).