Can I adjust the pressure of the wood pellet mill to pelletize different materials?

Maybe. It's not as straight forward as just pressure. Wood pellets form because wood contains lignin, which acts as a natural binder to hold the fibers together. During the pellitizing process, the lignin softens and sticks the wood powder together forming a pellet. If you wanted to pelletize some other material, one of two things needs to happen. It either needs to be a material that sticks when compressed (many polymers and sugar based organic molecules will work) or you need to add a binder to keep things stuck together. Often you need to do both. What types of pellets do you want to make?