If you want to have a different logo for the site and/or merchandise then by all means go for it. Don't feel obligated to keep using the one I made if you don't want to, I won't be offended if you want to mix things up.I will keep Spedistran's one but I may have a second one for merchandise.
That said, if you want to create and sell merchandise that uses any of the graphics I've made for the site, you're welcome to do so completely free of charge. Like you can sell them on whatever you want and keep 100% of the profit, make official Onion Farms thongs, I literally don't care.