[dire_lobo]

Which option/variant are you using? If you're setting up your products with "options group type" set as "product variant", once you've created the option group, you can click on the product variant link and edit your individual SKU's...

IIRC, I've also added a hyphen at the end of the SKU when setting up a new product, and when I generate options, it automagically adds the option ID after that... but it's been a while.