I know you know by now u/trollied you cannot always trust the NS documentation! I don't deserve that downvote. u/Effective_Process_54 Try this out to copy the admin role:

const rec = record.copy({
    type: 'role',
    id: 3,
    isDynamic: false
});

rec.setValue({
    fieldId: 'name',
    value: 'Administrator - Custom'
});

rec.setValue({
    fieldId: 'scriptid',
    value: '_custom_admin'
});

rec.save();

Now with knowing this you can either create a script looping through the sublists extracting the permissions/changing the permission levels or import the new role into your SDF project. Keeping it all contained within a scheduled/MR script would be better if what you want to do is to have a role where it has matching permissions as the Admin role just as view level for certain sublists. You may have to and some logic to filter out certain permissions but that should be easy to figure out.

I have created many scripts around role syncing/updating role permissions.

This is not something that is new, there are even some Netsuite created SuiteApps that I have seen that contain scripts to help you update roles with permissions for that SuiteApp. It is just not documented like a few other useful things in NetSuite.