@Tibtom
Just thinking about changing birth certificates. If I was borne in Sussex to Scottish parents, lived in Scotland for 35 years, and self id in Scotland my birth certificate is still an extract of the sussex register. How does the Scottish Government change that?
There's no such thing as "Scottish parents" as "Scottish" isn't a nationality. If you were born in Sussex the fact your parents were
born in Scotland/ think of themselves as "Scottish" is irrelevant. The relationship between your parents and you is governed by English law. Should you or they move permanently to Scotland, Scots law will apply going forward.
There are differences between Scots law and English law in some fairly major areas- inheritance and family law is different; Scots law gives 16 year olds far more autonomy in Scotland; divorce is different (and easier) and succession to property is different.
If you were born in Sussex but move to Scotland on a permanent basis (become domiciled) Scots Law will apply to you. Hence Gretna Green marriages (which don't require much in the way of residency)
If you were married in England you can get divorced in Scotland if you meet the residence requirements. On your death if you are domiciled in Scotland the succession to your property will be dealt with under Scots Law regardless of your being born in Sussex.
The statute dealing with registration of births in Scotland is The Registration of Births, Deaths and Marriages (Scotland) Act 1965. England and Wales (but not NI) isThe Births and Deaths Registration Act 1953 (I think).
Holyrood cannot possibly have power to order the Sussex registrar to re-issue a certificate issued under the English legislation.
Of course the separatist argument will be some sort of nonsense about everyone's welcome here and you can apply for Scottish citizenship . That might get you a Scottish passport but it still can't force the registrar in Sussex to issue a new birth certificate.