Is there an ambiguity or am I missing a theme? I've solved the clues (I think?), including the themed ones; I know what the substituted letters are, and therefore the nature of the second modification. However, at least two of the substitutions are unchecked by other answers, and in at least one case there are two possible real words which fit the checked letters of the grid. Specifically, I have 1ac. (themed, unclued directly) possibly ending in O or E. Without giving too much away, is there any way of deciding which one it is? My apologies for such a torturous question.
Many thanks; that was my conclusion eventually but initially had the uneasy feeling I was missing something obvious - Indy Mag CWs are usually free of such irritations.