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The human functional connectome, derived from functional magnetic resonance imaging, is sufficiently unique and stable to serve as an individual "fingerprint", leading some to view it as a neural proxy of the self. However, it remains unclear whether this fingerprinting property persists following exposure to extreme or highly uniform environments. In a longitudinal study, male infantry soldiers and a comparison group of male university students each underwent four resting-state scans across key life milestones. We tracked changes in within-individual versus between-individual similarity in functional connectomes over time. Early military service was associated with a marked reduction in connectome fingerprinting accuracy among soldiers, driven by a temporary reduction in connectome distinctiveness relative to the group rather than by reduced similarity to the self. In contrast, fingerprinting remained stable in university students across the same developmental period. Reduced fingerprinting in soldiers was specifically linked to connectivity within the default mode network. These findings demonstrate that the uniqueness of the human functional connectome is not fixed, but can be substantially shaped by powerful, shared environmental contexts, highlighting the sensitivity of neural self-organization to social and institutional structure.