Hi candelariajr,
Can you give an example please, I don’t see what you mean by “set the alt tag” as links do not support the “alt” tag… 
By the way I see that the link_to_collection function receives an array of attributes in its second argument (props).
Edit: maybe the second part of this topic may help you: Direct Linking to Collection Pages Instead of Collection Previews in Thanks, Roy Theme - #2 by jflatnes