Protests are important social forms of activism, but can be inaccessible to people with disabilities. Online activism, like the 2017 Disability March, has provided alternative venues for involvement in accessible protesting and social movements. In this study, we use identity theory as a lens to understand why and how disabled activists engaged in an online movement, and its impact on their self-concepts. We interviewed 18 disabled activists about their experiences with online protesting during the Disability March. Respondents' identities (as both disabled individuals and as activists) led them to organize or join the March, evolved alongside the group's actions, and were reprioritized or strained as a result of their involvement. Our findings describe the values and limitations of this activism to our respondents, highlight the tensions they perceived about their activist identities, and present opportunities to support further accessibility and identity changes by integrating technology into their activist experiences.