There is however one detail, what is passed must be internally consistent with other legislation otherwise it will fall at Judicial Review. For example if you want to pass legislation that contravenes the UK's Human Rights Act, you need to include a "notwithstanding" clause to show the courts you intended to override that law.
They could pass a bill to vacate these convictions quite easily but unlike the Buggery Act and Offences Against the Person Act 1828, they still want to be able to prosecute and protect the convictions of a subset of these people who actually did commit false accounting so the legislation is going to need to be more complex.
Only certain legislation, and that is in doubt after the Act of Union with Ireland case.
Generally the rule of Implied Repeal applies. Later statutes trump earlier ones.
Or that Rwanda is a safe country for migrants?
There's no way reasonable doubt remains, what is the legal barrier that an appeal court is trying to deal with?
> But these would be largely symbolic acts because the government can't, at the stroke of a pen, quash a conviction
This is untrue. Judges may not like it but I don't really care. The parliament is legally soverign and the courts are subservient to interpret and apply the laws as written in the legislation. If they write a law that says these convictions mean nothing, then they mean nothing.
Common law constitutionalism is based on the fact that individual rights exist - not the right of a judiciary to have separate powers.