If you really want to change things, you can write to your Senator or suchlike about racial inequality you have observed, or immigration reform. That is much harder than just grepping a codebase and submitting a PR -- but if you do it, you might actually effect change (and as a person of colour, I would be much more grateful to you, if you are from a more privileged class).
Your suggestion is to do something that will hopefully have some sort of macroscopic impact. That's great and should be done, but it doesn't mean that the microscopic impacts don't matter. I'm concerned about the actual small set of women that I work with on a daily basis not being marginalized.
You grep your codebase of choice for 'him', s/him/them, fire off a pull request, and think "Nice! I really did a lot for the advancement of minorities in tech today!", and then go out for drinks with your mostly white coworkers, where you discuss diversity in the workplace with a straight face.
Posting on hacker news an starting a flame war might cost a lot though.