Just my $01, but my concern with a piece of meat as large as a butt is the flavors of the spices would be diluted due to the high ratio of non seasoned meat vs low quantity of seasoned outer bark.
Most meat in Thai dishes is either stewed as in curries, or grilled. I think you will get way more flavor mileage using a spice slurry on smaller, thinner cuts of beef, pork, or chicken than on a butt. You could also try it on ribs, which I've done successfully in the past. Base ingredients I commonly use for this kind of wet rub or paste include serrano chiles or Thai bird, cilantro, mint, garlic, ginger, sea salt, soy and fish sauce.