Occupations are the jobs that are within the character's class, so yes they could be promoted and switch between occupations. That is entirely an in-character subject, so you're not going to be receiving messages from staff saying "Hey, your character was promoted" as you are the one to decide what they do and what happens to them. You can indeed switch occupations, for example, it is ICly common for youngsters to start as explorers before going into more dangerous occupations when they're older and stronger such as a foot soldier.

If you have any more questions, do not hesitate to ask! No such thing as too many questions unless you're Russ ^^