Have there been cases where a team leader made changes or wrote code independently?

Yes, in some teams, the leader may make changes or write code independently. This often occurs in small teams or startups, where the leader combines the roles of manager and developer. The leader may also write code to demonstrate approaches, quickly prototype, or fix critical bugs.

However, in larger teams, the role of the leader is more focused on planning, coordination, and quality control, with developers writing the code. In any case, the leader's involvement in the code helps to better understand technical details and maintain communication with the team.