Highways Sync allows you to designate a system as 'read-only'. This means that no matter what, no Sync will be able to perform certain updates to that system.
Important: This setting applies to custom fields and ownership assignment only. If you need to disable other options, for example, contact creation please disable those options for a given sync.
To enable read-only operations, click Applications, choose Settings and enable Read-Only:
Don't forget to click Save when you are done.