You could edit that cache file, but once you purge the cache, your changes will be erased and you'll have to reapply them.
It would instead be better to modify the template file for your style. I would assume you are using the prosilver style (or another style based on it), so go to the following file:
styles/prosilver/template/posting_editor.html and there you will see the code for the smiley box. Under that DIV, you can add your code for the list of car icons (similar to how it was in the cache file you edited).