I do believe that avatars and usersnames give off a subtle impression. Because it's your online identity after all;The closest thing you can get to showing a face and name without giving your real face and name.
Usernames seem more useful for identifying someone, But the emotion that a avatar or a avatar/username combo is expressing can does give me a subtle vibe of who is posting, Like what the op said about randomman's recent change that is making him seem less intimidating, And among other things about the poster like what series or meme they enjoy or what their gender is.
I can tolerate someone just changing there avatar if they atleast keep the username, but making a complete username change can get my head spinning, which is likely why had kept my username and avatar combo the same since I joined.
I only change my avatar around once a month (which I've kept to be just different pokemon fanart of a dewott) and I've only changed my username from "Notsocoolguy" to "Notsocool the Dewott" to individualize myself from other "notsocool" guys on the internet using that username as well, with the fact that my avatar is a dewott.
Fandom avatars? There's no reason why I should judge someone to be good or bad because of the sole fact that they have a furry or pony or sonic or whatever fandom their avatar is. But when I see someone in the comments using a roblox avatar, I have a impression of that user similar to how I see the rest of the roblox community (Spoooiiler:My experience with roblox doesn't make my impression 100% positive.)
But since seeing them is just incidentally, I just ingore them. And I don't hold the smallest bit of a grudge for any other fandom, because for the most part;I'm simply not a critical person.
In conclusion, The little image that is place beside our username is just the "cover of our book"; While the cover can give an impression of what it contains and show a grain of truth, the cover itself is not the whole story. A person who has an "intimidating" looking avatar is not utterly limited to posting that auditude.
But just because we shouldn't judge a book by its cover doesn't mean we never do so.