Unless something has changed recently, you can. Last time I played "Tales of a Sea Hawk", that's exactly what I did. I started off as a merchant character (possibly by default), which meant I had a Merchant Licence right away, and then I bought a LoM from Silehard at the first opportunity. Later on I got Dutch and Portuguese LoM's as well. Raiding enemy ships, and later on raiding colonies, made me stupidly rich, and the Merchant Licence meant I didn't need to share it with the crew.