That would be automation and is not allowed. Specifically -

This is why multi-boxing is just fine.

The moment that single keypress initiates a string of actions not normally possible via our base macro system for an individual character, then that is a different matter.
So, to expand your definition: ‘safe’ multi-boxing commands are one button press = one action per character.”
The point is that the ‘something’ that occurs spools out without direct human involvement aside from the initial pull of the lever. That is automation. Even if it’s only a single extra step.

In multi-boxing, every action taken by those characters has its source in a human command. Each individual action. Thus, it is not automation.
Multiple key presses/uses of abilities from a single command, spoken or typed? Not okay.
Setting up a macro with said keyboard that would, for example, automatically press Fireball each time it was available? Automation.