Changes
Mod tooling. I'm a UX guy, and I cringe when I have to deal with legacy code that I wrote. The mod tools make some of that look downright elegant. They sometimes work. They are sometimes spit and baling wire. In some cases... nobody apparently thought they were important (seriously, that should be embarrassing that not even CMs had tools for that).
The mod working group for tooling (see the Mod Team or Teacher's Lounge) is probably going to drop a giant list in your lap. It might even be wrapped in a knitted blanket that Tinkeringbell wraps it up in. But there are some tools that really really need updating, fixing or writingbuilding from the ground up. There should be some low-hanging fruit you can knock out for easy wins, as well as some that are just needed.
Don't change
The current bug list system. What has helped a lot is the visibility that status-review is actively being worked across SE. It might not be ideal or exactly what we'd pick for priorities, but it's actually nice to see that list go down and that Devs and CMs are retagging as needed and reporting overall efforts. It probably could be better, but it's not broken right now. Don't fix it.