Easier yet, you can set product-specific affiliate settings by going to Seller Admin > "Setup product specific affiliate programs", select a product and click "Edit Affiliate Settings".
The share percentage you set there will override the common affiliate share percentage for all sales of the selected product, EXCEPT for 0% which means the same as "no product-specific percentage" which means the common percentage WOULD apply to sales of that product.
If you have a common percentage set in Seller Admin > Edit Affiliate Program Settings, then it is not possible to completely exclude any specific products from granting any commission at all. The only way to exclude specific products from granting commission is to set your common percentage as 0%, then add a product-specific percentage for each product you DO want granting a commission.
If you do that and still prefer to issue only one, common Hop Link to your affiliates, you can go to Seller Admin > Edit Affiliate Program Settings and set the common percentage as 0% but provide a Common Hop Link URL. Then when you setup the product-specific percentages, leave the product's own Hop Link section ("Affiliates links will link to a page on your website") UNchecked.