This is not the uninstall password but the password to stop the service Symantec management client.
They should be the same however.

The easiest would be if you remembered the password, else I suppose you could start in safe mode and change the sylink file, The password will go away when the client gets the new policies from new SEPM

You could also try and set the Symantec Mangement Client service as "Disabled" and restart the machine, replace the sylink file and restart SMC

Lastly you could contact support to get the Cleanwipe tool and run it, then install a brand new client package

I can not think of simpler solutions right now

I have the password, I was trying to find out if there was an automated way of doing the replacement of the sylink.xml file to remote clients without interfering with the end users day.  My goal is to get them all pointing to the new SEPM console.  I have run cleanwipe on a few in a pilot group but I just needed a remote utility to change the settings to get clients to report in to the new sepm.

Do what Vikram said and used the Sylink Replacer tool, that should work fine for you provided you have an English Windows environment