Learn Portuguese (Portugal): Pretendo mudar de emprego este ano.

Pretender is a classic false friend. It means "to intend" or "to aim to do something." If you want to say "I pretend" in Portuguese, you should use the verb fingir.

Why do we need the preposition de in mudar de emprego?

When you talk about changing or switching one thing for another of the same kind (like a job, clothes, or a house), Portuguese uses the structure mudar de followed by the noun. Without de, mudar usually means to physically move or to alter the characteristics of something, rather than replacing it.

The English translation says "change jobs" (plural), but emprego is singular here. Should I ever say mudar de empregos?

You should stick to the singular. In Portuguese, the phrase mudar de emprego treats the concept of a job as a general category here. Saying mudar de empregos sounds unnatural because you are only moving from one single job to another single job.

Is there any preposition required between Pretendo and the next verb mudar?

No, the verb pretender connects directly to the infinitive of the following verb. Unlike verbs such as gostar (which takes de) or começar (which takes a), you never use a preposition after pretender.