For the first part, since you’re adding things to the existing category titles there are a few places that you could inject extra html via plugin component:
You can use this theme component to get an idea of where you can input things to your site:
This section goes into more detail on how you can add items to plugin outlets:
As for changing the names on the sidebar…here’s the code that controls that:
Overriding this function to something like
get text(){
return "..."+this.category.name.substr(-10)
could work for you, but that requires modifying core javascript, outside of a template. A small change like this is probably harmless long term, but you may run into difficulties when discourse updates.
If someone with more insight than myself wants to chime in I’d listen to them.