When you create an add-in Visual Studio, you will see the default set icon as a smiley. May be your requirement needs some other proper icon to be used. The question is how to change the default add-in icon easily.
Solution :-Open a solution that was created by using the Add-in project type.
-Open the Connect.cs file and navigate to the below shown line in OnConnection() method.
Note the number "59" in the line where the Command object is initialized. This is considered as the index of the current icon of the add-in. You can change this number to a different standard icon to get a new icon.
It is simple as that. Further more you can refer the below shown list to identify which icon stands for which number you specify.
You can see the complete list from the below reference :