Just figured it out. If you select "Adjust Difficulty" and increase the max gadget size (number of instructions that can fall at once) you change their order with these keys.

P.S. thank you for nerd sniping me with this game, I love the idea and execution (pun slightly intended)!

Thanks for the kind words! This comment helped me realize that I had misunderstood the parent commenter's question.

I have just pushed an update so that the up/down arrow keys only show up in the instructions if the max gadget size is greater than one.

Yeah, I may have sacrificed clarity for concision in this case.

To answer by way of example, if you are given "add R1, R2, R3" rotating to the right will result in "add R2, R3, R4". As another example, rotating "mov LR, R0" to the left will give "mov R12, SP".

In other words, rotating right changes every register RN in the instruction to be the register R(N + 1). Left changes RN to R(N - 1).

My hope was that if it was not clear from reading, it would be after testing things out. But hearing that this may not be the case is helpful feedback!

Oh, my bad, I misread your question.

See a reply to your original comment: it changes the order for gadgets larger than one instruction. The default is one, but originally it was three, so the instructions stuck.

I will make those confusing instructions only show up when the gadget size is greater than one! This feels like a good change to make based on this feedback.