I've completed the grid but am struggling with "The next line suggests..." changes. This line indicates changing one SPECIFIC letter for another SPECIFIC letter, but NOT also the other way round which seems to be necessary to complete the final instruction.
If one assumes that the word "changes" in the instructions can be construed as "EXchanges", this would work, but I have TWO "exchanges" in 35dn in order to leave a real word, giving me an odd number of swapped letters...
Am I overthinking this? And are there two exchanges in 35dn?