We are using CA SDM 12.6
Can we stop all mails (status update, survey, created, log comment) sent by SDM for a particular category?
Assuming that you are referring to emails and surveys sent by Activity Notifications, you can stop them for a particular category by adding a rule to the Activity Notification for Change Orders for each of the above activities. Test a site-defined condition along the lines of 'change category is not xyz' before allowing the email.
Yep, Notification Rules should allow you to do this kind of logic...