When a site owner, or someone with the right permissions creates an alert template on a list, every alert created after that uses this template by default.
However, if a member wants to, he/she can still create his/her own template. In this case, the site owner wants to control what information is sent by e-mail, so it would be a bad idea if members can put anything they want in an alert.
My solution: as a site owner, create the template. Make a new permission level for this specific list, where members can not create alerts. Then (site owner) make an alert for the members (alert for sharepoint group).
This sort-of works, but is not an ideal solution, I would prefer it if members can still create alerts, but not choose or make their own template. Is this possible?