Fantastic puzzle from Ifor, and really enjoyed reading about the work in question. I do have two queries, though....
39a - Stacked hand critically, with large number left in end (6)
I have the answer and know the extra letter and can see that the first 3 letters are "hand", but for the life of me I cannot see how the final 3 (pre change) come from "critically, with large number left in end".
I'm assuming the character "free to go" is the 5 letter one, but after he is erased it leaves 2 unchecked letters - do we just put them in the order they appear in the unaltered word? Also, the preamble says that the changes create new words but, after the character's been erased, the remaining 5 letters don't make a word - they do make a 2 letter one and a 3 letter one but as there's no line separating them it doesn't seem right?