The structure is clear in England and Wales.
The Sentencing Act 2020 sets the purposes of sentencing. That is a matter of policy.
The Sentencing Council, by dint of the powers it's given by Parliament, then writes guidelines for the judiciary. This is done by the members of the Council who include civil servants and the judiciary.
They cannot change the primary effect or intention of primary legislation by their guidelines or the policy. They need publicly consult.
So they cannot say, this guideline or it's application, should omit or otherwise adjust the purpose of legislation.
What you have just told me is alarming. It suggests that in Scotland, you can adjust sentencing law without a primary legislative change. A court may approve a guideline but without a decision on policy, a primary legislative change to reflect that, it looks like a criminal justice system administered a policy change, which would change the application of the law, without any serious scrutiny. A court is not a form of scrutiny. It presumably can only ratify what is in front of it.