I was investigating a new server I'd been assigned, looking for gaps in configuration using the trusty sp_Blitz tool. The organisation that owns this server instance is small and doesn't use third-party monitoring. I decided to add some basic alerting as recommended by Brent Ozar and Co. They've kindly provided a script to do this: Blitz Result: No SQL Server Agent Alerts Configured.
A little later on I realised that I needed to add an additional operator to these alerts and was loath to step through them one at a time and tick the appropriate box. So, I knocked out a quick and simple script (I've included two versions, one that adds the operator to all alerts and one that allows you to select a subset). I hope it is helpful.