I guess it varies from person to person. If somebody fixed something I wrote without asking I would be thrilled! I recognize that I am imperfect, limited by time, and striving to move to more impactful projects so I would be more than happy if somebody wants to improve a system I was inexperienced with or didn’t have the time to fix. I would probably give them the low down on the system and try to transfer maintainership of the system to them.

Reading the GP comment (going skunk), I wondered if the factors behind that turning out positively was the position of the fixer relative to the code/systems in question. If they're not stepping on anyone else's toes it works great.

This comment echoes that sentiment a bit, I think; there's an implicit dependency in there on the project not having a collective structural investment, whether that's explicit (overt, with explicitly delineated boundaries) or implicit (implied, fuzzy, part of collective culture), on the thing being fixed.

Yes! I agree. Best to fix up code of people who are long gone instead. No one else will touch it so no merge conflicts either! Just make sure the fix makes others appreciate it. The populist fixes are fixes in dev tool chains that everyone in the team will appreciate. If you want a hobby just make any part of CI faster for some love from the team.

In a healthy team no one person owns an area of the code, and most complex areas are a weird amalgamation of several people's commits anyway. I haven't worked with anyone who takes fixes as personal insults for a very long time.