I've been asked if its possible to get alerts from the website whenever there is an update. The alerts will be emailed to a user group, which anyone can sign-up to.
At basic level this could be achieved by creating a trigger that send out email to the user group when the asset status is changed from safe edit to approved to go live, however sending email to 100+ users (could grow more) kind of worries me a bit, and to complicate things further the alerts would be based on the options they have ticked during sign-up.
Just to clarify, you want a user to be able to sign up to a usergroup themselves in order to then be sent updates?
As you said, a Trigger can do this to notify a particular usergroup(s) or individual users when an asset is created, updated, status change,etc etc.
So your question is more in the strain of "Can I allow a user to add themselves to a usergroup (without the user being an editor)"?
If they do not already have a user account, and where to select the option to sign-up to updates, using an Account Manager Page asset you could set it to allow them to choose to sign up to the updates (i.e. create a Selectable Locations setting for the usergroup)
An account manager page allows a user to login and modify/update their own details (name, email, etc) I believe; however, I have never used one other than whilst doing the Squiz Training!
I don't think this would allow an existing user to add themselves to a new group though.
For an existing user, I think this is what you are looking for: User group manager page
"A User Group Manager Page allows users to link themselves into User Groups. For example, you may want to allow staff members to update their position in the organisation by adding themselves into various User Group."