However not via any self serve option, this is something which professional service have to do however they can do all sorts of things like this... I, a couple years back got them to identify all users without a custom avatar "the ones using stock ones" then randomly assign one of 20 brand new avatars i'd build then remove all default Khoros avatars.
Personally, i feel the out the box avatars are flat and did not align with my brand and so i made my own and forced the change across the site so that my shinny new site didn't have ugly avatars
You can also assign the exact same avatar to each new member as they join or you can randomise an avatar for each new members which makes more sense. I then, possibly had taken it to the extreme by building a profile wizard which allowed for easy update of avatar along with encouraging them to fill in their profile.
However not via any self serve option,
That's what I was afraid someone would say. Not that I'm blaming the messenger! [grumble grumble.....wish it was SQL instead of LiQL] I appreciate the reply.