The work of hymn revitalization mainly concerns archaic expressions and words that no longer plainly convey meaning to the singer. The most common offender in this respect is the use of Thou/Thee (or Ye) for You. (See separate discussion on the error that can be perpetuated to the modern Christian by such usage.) Other common issues are outdated verb forms (DOTH, GIVEST, SAYETH, etc.), archaic words (AYE, BUCKLER, FAIN, TRYST, etc.), or words no longer common in the sense used (SMITTEN, etc.).
When a word or phrase has become so archaic to warrant alteration is a judgment call. The users of this site can decide for themselves to what extent alteration of the lyrics is warranted. This site further advocates for hymn RENEWAL, not just substitution of a modern for archaic term. Where the rhyme scheme of the verse is impacted by lyric modernization, otherwise unobjectional lyrics thus often need to be changed in order to preserve the rhyme continuity for the contemporary singer. In such situations, the goal has been to find new language that remains faithful to the original OVERALL message of the author. In some instances, more conservative and more aggressive options have been offered. In general, a conservative approach has been taken.
It should be noted that in the past, lyric revision has been motivated primarily out of concerns for "doctrinal purity." In this site, NO CONSCIOUS ATTEMPT HAS BEEN MADE TO ALTER LYRICS FOR DOCTRINAL REASONS. This said, the site has sought to suggest alternatives to some unfortunate lyrics (“Sad, that bitter wail”). There has also been occasional efforts to clarify lyrics that could easily be misunderstood. (The Psalmist, for example, was not suggesting that believers "flee as a bird to your mountain"; instead, we are to "go to the clear flowing fountain," but the lyrics likely fail to make this choice clear to the modern singer.)