A mapped key has a few ingredients.

Most have a hotkey to activate them.
Although they don't need this, if they'll only be activated by another mapped key.

They usually do one thing.
IE, have one step.

If you wanted a mapped key on the " ; " key...
You would probably make a new mapped key.
Use the ; as the hotkey.
And have it output (in actions) the ; key to all windows.

In the case of Mercurio's macros.
There is a spam key, which can be '2' or whatever you want to spam.
This is the hotkey for the mapped key.
It has two steps, because it does one thing on the first press, and something different on the next press (at which point it resets to the first press).
He has chosen "2" as the output of the first press, and ";" as the output of the second press.
But "2" is the only key which is pressed, and it will likely be spammed.
If you always want the "proc" on this is a decent way to do it.

If you want to be able to disable it.
You'll want something like the approach you linked in green.
I'd have a mapped key, using whatever key I wanted to spam.
And have it "Do Mapped Key" twice, once for each output.
Then have a toggle macro (two steps) one that enables the second output and one that disables it.
So you can spam the "spam key", and have it alternate outputs or just output the one key.