I was feeling confident about addressing the second part of the endgame when I posted #107 yesterday. Sheer hubris, punished by the gods who dwell on Mount Listener!
I slogged my way through putting the redundant letters into grid entry order, but I didn't have a skooby how to interpret what replaced the contents of most cells AND the second instruction.
Ater a frustratingly long time, I finally realised that I had made my usual mistake of writing down the wrong redundant letter — TWICE — once in both parts! I found the first in the two-letter word which unfortunately made it a verb instead of a preposition. Once amended, the penny dropped and I was able to forge ahead with the slog of replacement. This led to the message in the unreplaced cells, which in turn led me to amending what looked like a string of jumbled letters after the first word of the second instruction into two separate words.
After all this, I'm still not clear how "extending the second instruction" to the letters unreplaced gives the required result; surely it's simply the first word of the second instruction that should be applied? Is that correct, thus leaving the grid clear for what left some posters here "cold" and leading to the Marmite-effect mentioned above?