Yes, you can add a ternary into the append
call:
return $( "<li></li>" )
.data( "item.autocomplete", item )
.append( (item.address != '')?("<span class='customer_search_addr'>" + item.address + "</span>"):("<a>" + item.label + "</a>") )
.appendTo( ul );
Hovewer, it's quite messy, so i would do it like this:
var address = (item.address != '')?
("<span class='customer_search_addr'>" + item.address + "</span>"):
("<a>" + item.label + "</a>");
return $( "<li></li>" )
.data( "item.autocomplete", item )
.append(address)
.appendTo( ul );