Without hesitation, I'd proclaim I could easily make those changes!
Then I'd load their site, load their plugin/theme code and css files, struggle for hours to get the desired effect, and even if I got it to work, I would break every other part of their site.
---
Denigrating anecdote aside, good job Matt, loved the story at the end.
Once you spend some time in the codebase and understand a bit of its legacy history it gets easier over time. A lot of plugins and solutions are aimed towards non-technical users and a lot of overlap. Where we might just write up some custom HTML others might install 3 plugins to make it work.
Thankfully there was a recent consolidation in a plugin called Admin & Site Enhancements (ASE). Probably got rid of 10 others with this thing. Includes duplicate post/page, admin menu cleanups & reorganization, hiding dashboard widgets, cleaning up the top bar, changing the login URL, an easy way to setup SMTP delivery, media replacement, hides the annoying admin notices, and a bunch more.
A lot of the stuff you want to do can be maintained at the command line. And it even gives you a way to do some fleet management.
I am not against wordpress in general, just that I found it not suited for my purposes.