Thank you for reaching out to us.
There is no way to disable directory sync for few users in Azure AD.
Directory sync is enabled at the tenant level either you set to true or false at the tenant level not at user level.
Note: If you use this command, you must wait 72 hours before you can turn directory synchronization back on.
Only way you can update the synced user ( properties ) is from on-premise AD via Azure AD Connect.
Let me know if you have any questions.