The social identity approach asserts that self‐categorization is fluid and created anew in context. Despite this, research often conceptualizes identities as being based on static categories. In this article, we assess: how attitudes may be relevant attributes used to categorize the self and others, and therefore have the potential to foster social identification; how such categories/identities can be updated with new attitudinal information; and how attitudes have greater impact when socially expressed. Across three preregistered computer‐mediated interactive experiments (N = 3087), involving attitudes relating to the Ukraine‐Russia conflict of 2022, we find, identities can be updated with the introduction of new attitudes in interaction; cumulative attitude congruence strengthens identification; attitudinal interaction strengthens opinion‐based group identification and activism intentions, and ingroups can strategically align their attitudes. We conclude that to fully understand identity formation, we must acknowledge the fluidity of self‐categories and resultant identities, in line with the original specifications of the social identity approach.