If you want to exclude any product(s) from earning affiliate commissions, you would first need to have a 0% common affiliate share in Seller Admin > Affiliate Program Settings (you can still define a common hop link URL if you wish).
Then edit product-specific affiliate settings to define a share percentage for each product you DO wish to grant commissions on (you can set those %s without necessarily also configuring a product-specific hoplink URL, if you only want to issue common hoplinks).
You can replace our standard button image with any custom button image you wish, as explained here:
http://www.e-junkie.com/ej/help.custom.purchase-buttons.htm