Anecdotal evidence suggests that songwriting assists people with spinal cord injury (SCI) or acquired brain injury (ABI) to explore threats to self-concept, yet studies that explore the mechanisms of change have not been reported. In a pilot study, we explored the correlations between changes in self-concept and well-being, with mechanisms of flow and meaningfulness of songwriting. Five people with ABI (all male) and 5 SCI (4 males, 1 female) (mean age 38.90 years, SD = 13.21), with an average 3 months post-injury, participated in a 12-session songwriting program that targeted examination of self-concept. Measures of self-concept, depression, anxiety, emotion regulation, affect, satisfaction with life, and flourishing were collected pre-, mid-, and post-intervention, and compared with repeated measures of flow and meaningfulness of songwriting. Medium effects were found for changes in self-concept (d = 0.557) and depression (d = 0.682) and approached a medium effect for negative affect (d = 0.491). Improvements in self-concept over time were associated with decreases in depression (rp = −0.874, n = 9, p < 0.01), anxiety (rp = −0.866, n = 9, p < 0.01), and negative affect (rp = −0.694, n = 10, p < 0.05), and an increase in flourishing (rp = +0.866, n = 9, p < 0.01) and positive affect (rp = + 0.731, n = 10, p < 0.05). Strong experiences of flow were not positively correlated with positive changes to self-concept and well-being, whereas deriving high levels of meaning were associated with increased negative affect (rp = +0.68 p < 0.05), increased anxiety (rp = +0.74, p < 0.05), and reduced emotional suppression (rp = −0.58, p < 0.05). These findings show that the targeted songwriting intervention appears to be positively associated with enhanced well-being outcomes. However, the findings also suggest that people who find the songwriting process has strong meaning for them might be more likely to start accepting their emotions and as a result experience an increase in anxiety and depression, although full, mediated regression analyses with larger sample sizes are required to explore this further. Acknowledging their changed circumstances may nonetheless assist people with SCI and ABI to grieve their losses and facilitate the building of a healthy post-injured self-concept. We propose that there may be other mechanisms more critical in facilitating the positive changes in self-concept and well-being than flow and meaning, such as the role of story-telling and the impact of music in facilitating the consolidation of self-concept explorations in memory.