Some thoughts about ego, flexibility, and imitation in writing for money
I think my biggest recommendation to someone new to the career of writing for money, specifically in a field like games where you so often write with a team of other humans, is: learn how to imitate others. You gotta learn to write the way other people do - in particular, the people on your team, with whom you share your project and your goals. If you don't learn to imitate one another, you'll be unable to speak with a shared voice.
Doing this requires you to discard, as best you can, the idea that your writing always represents or illuminates some part of your own soul. This can be hard to do after learning the kind of stuff they teach you about writing in school. The idea that writing needs to express your soul can make tone flexibility feel like a betrayal of self, for some people. I do agree that writing is an expression of thought - but it shouldn't always be an expression of ego, too.
It got easier for me to switch off my ego and imitate others when I started thinking about how each writing assignment I get is fundamentally insignificant - at the scale of a lifetime, anyway. My life will be long, writing-wise, and I will have many, many opportunities to express different facets of my life and my self in my writing. So I choose to tell myself that each time I write, nothing is at stake; no part of my soul is on the line. I am, actually, just acquiring experiences. I learn a lot from flexing to meet writing partners where they are.
Learning to imitate others means learning to understand them. If you learn to match the writing styles of the people in your team, you are learning to read their work closely, to identify its strengths, and to negotiate with them about voice and style.
This also means that you gotta discard the idea that any individual asset in a game belongs to you, or that the writing you do for the game represents yourself. The writing I do for a game is our writing, not my writing; it's the game's writing. Its strengths and weaknesses emerge not from the strengths and weaknesses of my soul, but from the strengths and weaknesses in the relationships I have with the team.
I understand that it is hard to see someone on your team rewrite work you were proud of; I really have no solution for this except to encourage you to, deliberately, practicedly, forget which work you did for the game. I am not joking. By the end of a game production, I like to try to forget almost all the work I did. I want to see each part of the game as something we built together, so I try to surrender it.
It takes a lot of practice to write this way, but you can do it. And learning to imitate other people's writing can genuinely be a ton of fun. It's like wearing a costume at a halloween party. Nobody is ever going to mistake the work you do matching another person's tone or word choice or style as some reflection on your soul. The people who work in this business will see it for what it is: careful, practiced skill, full of sacrifices you made for other people.
You are always learning something when you spend time learning to imitate. And the stuff you make together in the end will just be better and more focused and more interesting - particularly if this is something you learn together, on purpose, as part of your respect for one another.