I added a new Dialog to my Interface plugin for Virtools Dev 3.5. It allows to quickly delete all attributes from one or several categories. The standard attribute manager moves the attributes if you delete the category but does not delete them.
In 4.0 you now have the possibility to delete all unused attributes, but I think Matthew said, that it doesn't consider attributes used in VSL scripts – what might be tricky to support. I don't know if this was changed for Virtools Dev 4.0 SP2, but 3.5 users have now better control anyways.
p.s. here is a little chat log from the IRC channel, maybe it helps if you are unsure how it works:
[15:47] LeDom: ok, it takes less than 20 seconds to free you from 470 attributes
[15:47] LeDom: just did a test with one of our projects at work
[15:48] LeDom: a) install DLL
b) start dev 3.5
c) load CMO
d) open main menu -> Dom's -> "Delete Attributes by Category"
[15:49] Vsaiwrk: nice.. thats a lot faster >:)
[15:49] LeDom: e) hit the button "select all"
f) click on the categories from your project to deselect them
[15:49] LeDom: g) hit the "->" button
[15:49] LeDom: h) click DELETE button i) close the dialog
[15:50] LeDom: k) go to the attribute manager j) if it still shows all the attributes, close it again and reopen it
[15:50] Vsaiwrk: have to close and reopen the attribute manager if you already had it open still
[15:50] LeDom: (yeah f5 doesn't work here)
[15:51] LeDom: l) open "-No Category-" tree/section
[15:51] LeDom: j) select all the attributes in that section using shift
[15:51] LeDom: l) hit "del" key
[15:51] LeDom: m) done, enjoy, relax be happy
[15:51] LeDom: 😉
[15:52] Vsaiwrk: deleting the category deletes the attributes in that category also here.. you're saying it should put them under no category?
[15:53] LeDom: ?
[15:53] LeDom: no, but you may have some there by default
[15:53] LeDom: it does kill them all but no category is no category and therefore not touched
[15:53] LeDom: by my dialog
[15:53] LeDom: maybe i need to add a button for this too
[15:53] Vsaiwrk: gotcha