We have this scenario come up quite often - where contracted workers may convert to be permanent employees.
We have a process setup where the Username/User IDs are basically switched between the accounts. We had a look at the Merge User Moodle Plug-in, but was warned this may cause errors, particularly with Programs and Certifications.
Our process is slightly different to how this could work for you, as the converted workers usually keep their Username, but their User ID (Payroll ID) changes - but you should be able to change the new profile to a temporary username/ID, and then update the old profile.
This process allows the HR Sync to do it's thing still, but has the full RoL against the profile you want.