The Immovable Rod's definition (DMG) says, in part:
This flat iron rod has a button on one end. You can use an action to press the button, which causes the rod to become magically fixed in place. Until you or another creature uses an action to push the button again, the rod doesn't move, even if it is defying gravity.
How might one activate an Immovable Rod at a height? Any spell, class or racial feature, or other effect based in the 5e canon is worth discussing.
The specific height is immaterial. Assume the Rod is on a stick.
Also, is there any RAW reason that attaching a pull string to some sort of hinged push thingee wouldn't work? You know, to push the button when you pull the string?
As a counterexample, what won't work is mage hand, since the spell says it can't activate a magic item. As a GM, I'd disallow it, but I'd be open to arguments for why it would work anyway, although cool as moving and activating a Rod with mage hand would be, the Rule of Cool is insufficient.
And for you law-and-order types, this has nothing to do with breaking into castles. No sir. It's for hanging a pulley to load and unload wagons and ships and such. That's it. Loading and unloading only.
Bonus for a way to activate the rod at a distance using a bonus action or multiple rods on a turn.