quiz, what makes the puzzle coherent (for me, at least) is the process of 'defining' the items we're highlighting. The two titles we're dealing with don't do this - in fact they make a virtue of not doing so, and that's the whole theme of the puzzle, as I see it. So, we're answering an unspoken question by adding to, or changing, certain key words (the one you mention going from verb to noun, for instance) or we're cryptically showing the 'things' in action.
useby - I agree with your 100% assurance comment - not only that, we're told where to look, how many words to change and how many cells to highlight.
As far as the triplets go - yes, I struggled a bit with the name but I quickly got the end parts and I'd already arrived at the theme via the song title (I only needed the two most obvious triplets for that before the puzzle's title pretty much confirmed it).
The generosity of Ifor's synonyms was much appreciated after the struggle I had with the other musical synonyms a few weeks ago - I got absolutely nowhere with those until I'd cracked the theme (more by luck than design). I didn't even need a dictionary for Ifor's set!