I've made several fogger apps (without any code, so basically they're just hyperlinks in the unity launcher). How can I change the icon of these 'apps'? (Do I, for example, need to make a stylesheet?)
Well you could open the Fogger-App with an editor like Scratch and change the icon. This should look like:
You will have to change two app files one for the Launcher and one for fogger.
I use Slingshot on elementary OS Luna and had to changes these app files:
When creating a fog app, click on the icon left to the name & url field, then select your icon. Or: drag & drop an icon to the new fog app window.