Abstract: (1) Background: Data on combination or sequential treatment of spinal muscular atrophy (SMA) with disease-modifying drugs (DMDs) are missing and the latter field is poorly understood. The currently available data of patients on risdiplam previously treated with nusinersen are coming from exploratory research mainly focused on safety. Our aim was to investigate the real-world effectiveness (hypothesising non-inferiority) and safety profile of risdiplam in a paediatric-and-adult nusinersen–risdiplam spinal muscular atrophy switch cohort. (2) Methods: A retrospective and anonymous collection of relevant demographic and clinical data for all Croatian SMA patients switched from nusinersen to risdiplam up to September 2023 (reimbursed by Croatian Health Insurance Fund—CHIF) was performed using the CHIF database and associated reimbursement documentation. Patients were included in effectiveness and safety analysis if they met the following inclusion criteria: (i) risdiplam was reimbursed by the CHIF; (ii) the patient received at least six doses of nusinersen before the switch to risdiplam; (iii) there was no relevant pause between the latter disease-modifying drugs; (iv) availability of all prespecified studied data and parameters. (3) Results: In total, 17 patients met the inclusion criteria (58.9% female; median age 12.75 (3.0–44.5) years). In our ‘switch’ cohort, we demonstrated a non-inferiority of risdiplam to nusinersen in the SMA 1 (+1.0 in CHOP INTEND; p = 0.067), SMA 3p (+0.7 in HFMSE; p = 0.897), and SMA 3a (+0.8 in RHS; p = 0.463) subpopulations, during a one-year follow-up period. There were no reports on respiratory function worsening, feeding worsening, and no lethal events. No new safety concerns were identified, except for the weight gain that arose as a new potential adverse drug reaction ‘signal’ in two patients. (4) Conclusions: We have reported pivotal real-world findings on switching SMA patients from nusinersen to risdiplam and demonstrated its effectiveness (non-inferiority), safety, and tolerability in a heterogenous paediatric-and-adult ‘switch’ cohort; this will further increase the quality and standards of care as well as safety of a notable portion of SMA patients, especially for those who demand the switch from nusinersen to other DMDs for clinical or personal reasons.