You can change the image by changing the characters body reference.
This can be done from the
Character Object (or prefab) -> Human Body Component -> Body Type (dropdown)
If you make these changes on the prefabs you wont have to keep making these changes for every new character you create.
Project View ->Equal Reality -> Resources -> Equal Reality -> Prefabs -> Characters -> Select a character ->Inspector -> Human Body Component -> Body Type (dropdown)
A bit of follow up feedback here. During my most recent build, this solution worked like a charm for all characters in the library, except for Freddy Casual.
For some reason, the Freddy Casual Icon displays as Freddy Navy despite the correct Character Prefab / Body Type alignment.
Photos from the inspector found here: https://imgur.com/a/F3ADOg9