Stage 1 Registered Report submitted to PCI Registered Reports, revised following the recommender's review. Whether moving from paid employment into self-employment improves or harms well-being is contested, and within-person and quasi-experimental designs have addressed it but none is preregistered. This Registered Report preregisters a within-person fixed-effects analysis of the UK Household Longitudinal Study (Understanding Society), positioned as a specification-committed replication and extension, of how transitions from paid employment into self-employment relate to subjective financial well-being and to psychological distress (GHQ-12), with adaptation tested through an event-study specification and three preregistered moderators (necessity vs. opportunity entry; solo self-employment vs. employer; gender). Fixed effects absorb only time-invariant heterogeneity; event-study leads and a placebo bound the time-varying-confounding and reverse-causation threats, so estimates are associational. Family-wise error across the two primary outcomes is controlled by the Romano-Wolf stepdown, and an outcome-neutral gate downgrades any underpowered test to estimation-only. Secondary-data bias Level 4: data accessed only after in-principle acceptance; pipeline frozen.