It's supposed to shift focus from your identity to your actions. "I code for a living" / "I code often" or even "I like coding" are very different phrases than accepting the programmer identity/label. It's not about what you are, but what you actually do. Focusing on your actions instead of yourself is a lot less narcissistic.

I think the 'am' constraint is meant to force you to shift your perspective from an internal frame of what you think you 'are' to an external frame of what do you 'do' through actions to/for other people and the world in general. Maybe these actions support what would be on your 'am' list, but maybe they don't and that might be a hint that you may not be who you think you are.

I read the `practice this' part as meaning that you should actively be thinking more about how your actions affect the people and world around you, and less about how the people and the world are affecting you.