I dont believe this is possible and if you not i'd like to request this as a feature.
Some of my workspaces can have up to 28 or 30 sheets in them, all related to the same project.
As the owner i would like to be notified of any changes within these 28 -30 sheets, but dont want to have to repeat the process of setting up each individual sheet. it would be far easier to have the option of setting notifications as a group per workspace.
Many thanks