How to modify $core_v2_activityStory.ViewHtml

Activity stories are rendered from scripted plugins -- you can see the full list of implementations by going to Administration > Interface > Widget Studio  and selecting one of the plugins listed under "Activity Story Types" from the "Viewing" drop-down. Each plugin listed here represents a different story type. Community selects the appropriate plugin and renders its script based on the type of story being rendered.

Excellent; thank you!