Neck Rub by Ifor
All perimeter entries are words derived by modifying their clue answers in a consistent way. A two-word phrase, from which the puzzle title has been derived in the same way, must be written under the grid. All other clues contain an extra letter. Those extra letters in the clues to 4- and 5-letter answers, read in clue order, describe which non-perimeter letters must be identified; likewise those from clues to 6-, 7- and 8-letter answers explain what must then be done.