-- Enable an alert.

If Not Exists(Select name From msdb.dbo.sysalerts
 
Where name = N'yourAlertName')
 
Exec msdb.dbo.sp_update_alert @name=N'yourAlertName',
 
@enabled=0
 
Go


-- Disable an alert.

If Not Exists(Select name From msdb.dbo.sysalerts
 
Where name = N'yourAlertName')
 
Exec msdb.dbo.sp_update_alert @name=N'yourAlertName',
 
@enabled=1
 
Go