Just install a local mysql server and run an upgrade will get all OLD mysql data currently in the central mysql server synced to the local mysql servers?
No, this will not work as the data is synced from the datalog and most likely your datalog does not contain all needed data.
What you can try is that you install a exact copy of master database on every slave. Then use a config.inc.php file from the latest version (not your old version) and replace your config.inc.php file with it. Then you will have to set the correct login details for local and remote database in this file.
But I never tested this so it might be that it does not work.