A diagnostic report is professional evidence and advice. It cannot instruct a school to provide particular provision, and no recommendation is automatically binding.
A diagnosis also does not automatically produce an EHCP, statutory provision, or exam access arrangements. Access arrangements are decided by the centre, based on the candidate's normal way of working and the regulations in force, see the exam access arrangements FAQ and the free "what evidence helps" checklist you can share with the SENCo or exams team.
A report does not determine entitlement to a benefit either. If you are looking at Disability Living Allowance, DLA and dyslexia explains what a report can describe and what DWP decides.