Set default pdf icon with Foxit Reader
Once you have changed the default application using Get Info, you may need to clear the icon cache.

To get started, close all open applications and then launch Terminal from Macintosh HD > Applications > Utilities. Copy and paste the following command at the Terminal prompt and press Return to execute it:

sudo find /private/var/folders/ -name 'com.apple.dock.iconcache' -delete
sudo find /private/var/folders/ -name 'com.apple.iconservices' -delete
sudo rm -r /Library/Caches/com.apple.iconservices.store


Restart, job done.

From Safari download bar rar file icon show as VLC icon,which associate to The Unarchiver should shows its icon