Released in 1.6

Released in 1.6

Released in 1.6

Released in 1.6

Released in 1.6

Could you please describe what exactly you're doing to lock the program up? Are you using 1.5.7 or 1.6beta3?

If I understand correctly, this is actually already possible.
You actually can select more than one note via Ctrl+Clicking on them. Or if you want to tag all untagged notes, select "Untagged", then "Edit/Select All", then "Edit/Tag".
Or, from the keyboard [assuming version 1.6 Beta2+]: Ctrl+U, Ctrl+A, F4.