MacOS Calendar App - Default reminders For my calendar alerts, I like to receive reminders with sound: 


1 day before the event  
2 days before the event 
7 days before the event 
1 hour before the event


Is there any way to set these as default for all events that belong to a "calendar" group (by "calendar" group I mean the coloured label that you can apply to an event)

Going to Preferences > Alerts lets you set defaults, but not by calendar group (instead the same defaults are used for all calendar groups). It also only lets you set 1 default (so you cannot have multiple reminders per an event)
Not that I know of, but there's a potential workaround - I don't know whether this would be any use to you.


Make a new event, call it myDefault, set all your reminders as you want them to be.
Any time you make a new event, start typing myDefault - it will auto-suggest that previous entry, but at the date you double-clicked. It will fill it with the previous data, shifted to the new time. 
Accept it, then change its name.


You can set several of these, named appropriately - the one thing you can't do is dictate which calendar group they belong to, so you'd have to make sure to generate the name to match the group it's going to belong in manually.