Related Clues:

• Change suddenly, e.g.
• Make an abrupt change ... and a hint to this puzzle's theme
• Go into reverse, e.g.
• Go into a new mode
• Make a sudden change
• Go from neutral to reverse ... and a hint to each set of circles
• Make a sudden change, or a hint to the words transposed in 17-, 23-, 37- and 47-Across