Simple answer: Yes a character can change career at the end of any term.
At the end of each 4 year term you make a roll to continue in a career.
Page 74 has a note about Changing Careers and apparently refers to the missing table in the MasterTextOld.pdf so you've just identified errata.
I think however the reason the Changing Careers table was omitted from the final document is that it makes it really restrictive as to what careers you can transfer between. For example an Entertainer can never become a Scout, a Merchant, a Rogue, or an Agent (no Mata Hari in the 3I :O)
*fluff*
The way I'd handle it is if the player declares at the end of a term that he wants to change careers he can make the qualification rolls for the new career. Actually I might suggest that he make the continue roll so that if he fails to qualify for the new career he can continue, otherwise if he's resigned from his old career and failed to enter a new career of his choice I'd shunt him into the Citizen career.
*end of fluff*
Hope that helps.