While open source software (OSS) communities thrive on collaboration, conflicts such as toxic behavior and discrimination can surface, threatening the sustainability of these projects. To address these concerns, many communities have adopted a Code of Conduct (CoC) as a mechanism for governing and moderating members’ behavior. Previous research has explored the motivations behind CoC adoption and the content changes made, but it remains unclear how different communities are using and maintaining CoCs over time after the initial adoption and how the presence of a CoC impacts a community. To bridge these gaps, our study compiles a large-scale dataset of CoCs along with their change histories in OSS repositories on GitHub to quantitatively (1) understand the evolution of CoC content and identify change patterns across different communities, and (2) investigate the potential impact of CoC adoption on community engagement. Our results show that OSS communities with a CoC attract more new contributors and decrease the number of existing contributors disengaging from the community in the long term. The insights from this study provide guidance on best practices for maintaining CoCs in OSS communities and offer statistically significant evidence of their impact.