Halakhic appropriateness of changing a mechanical timer on Shabbos?

I have one of those mechanical timers where you lift a peg when you want power to go to the plugged in device and lower a peg when you don’t want it to flow (See example here.

Suppose I have a warning tray where the timer went on at 9am and it was set before Shabbos to go off at noon. Suppose at 10AM I realize that I actually need the timer to stay on for an additional hour. Can I adjust the pins on the timer to keep the warning tray on for another hour? What in doing in this case is causing the power to stay in it’s current state (on) for an additional hour. I’m not causing the power to go on or off.

EDIT: I found a web post that discusses this exact topic: https://www.dortikvah.org/post/timers-on-shabbos