This will require you to override either ChatPrinterPanel.cs or ChatMessage.cs (I suggest the latter) and listen to the OnAuthorChanged event to change or rearrange the ChatMessage prefab. If you are unfamiliar with overriding I suggest checking out the CustomUI example project (https://github.com/Naninovel/CustomUIExample) which has a ChatMessage override which adds timestamps to the messages.
This will also require an override of ChatMessage.cs into which you can include a string parsing system (similar to the timestamp example). Be aware that smilies are supported out of the box when using TextMeshPro (look up TMPro documentation for setting it up) but for any larger images, the override is necessary.