Depois do imprevisto, o agregado familiar mudou o orçamento.

Because depois normally takes the preposition de before a noun.

So the full structure is:

• depois de + noun

Here, de + o contracts to do:

• de + o = do

That is why you get:

• depois do imprevisto

Examples:

• depois da reunião
• depois do jantar
• depois dos exames

Using depois o imprevisto would be ungrammatical, and depois de o imprevisto is theoretically separable in form, but standard Portuguese uses the contraction do here.

Here imprevisto is being used as a noun, not just as an adjective.

It means something like:

• an unexpected event
• an unforeseen problem
• something unplanned

In this sentence, o imprevisto is a general way of referring to an unexpected incident or setback.

As an adjective, imprevisto can also mean unexpected:

• um problema imprevisto = an unexpected problem

But in your sentence, it stands alone as a noun:

• o imprevisto = the unexpected event / the unforeseen issue

Agregado familiar is a more specific and often more formal expression than família.

In Portugal, agregado familiar usually means:

• household
• the people who make up one domestic/economic unit

It is especially common in:

• administrative language
• legal language
• tax forms
• financial contexts

So in a sentence about changing a budget, o agregado familiar sounds quite natural because budgeting is often discussed at the household level, not just the emotional or biological family level.

Compare:

• a família = family
• o agregado familiar = household / family unit for practical or official purposes

The main noun here is agregado, which is masculine:

• o agregado

The word familiar is an adjective describing agregado, so it agrees in a form that works here as:

• agregado familiar

Because the head noun is masculine singular, the whole noun phrase takes:

• o agregado familiar

This expression is fixed and standard in Portuguese.

Mudou is the pretérito perfeito do indicativo, which corresponds roughly to the simple past in English.

It is the third person singular form of mudar:

• eu mudei
• tu mudaste
• ele/ela/você mudou

Here it means that the action was completed:

• the household changed the budget

It is not describing an ongoing or habitual action. It presents the change as a finished event after the unexpected problem happened.

Portuguese uses definite articles more often than English.

So o orçamento is completely natural here:

• mudou o orçamento = changed the budget

In Portuguese, article use with nouns is very common, especially when referring to something specific and understood in context.

Here, it is not just any budget in general, but the household’s budget, so o orçamento makes perfect sense.

Yes. That version is also correct.

Both are natural:

• Depois do imprevisto, o agregado familiar mudou o orçamento.
• O agregado familiar mudou o orçamento depois do imprevisto.

The difference is mainly emphasis.

Starting with Depois do imprevisto puts the time/context first and highlights the unexpected event as the background for what happened next.

Starting with O agregado familiar puts the subject first and sounds a little more neutral or straightforward.

Yes, mudou is fine and natural, but other verbs are also possible depending on nuance.

For example:

• mudou o orçamento = changed the budget
• alterou o orçamento = altered/modified the budget
• ajustou o orçamento = adjusted the budget
• reviu o orçamento = reviewed/revised the budget

Mudar is a broad, everyday verb and works well here.

One thing to watch out for:

• mudar o orçamento = to change the budget
• mudar de orçamento would suggest changing from one budget to another, which is a different idea

Portuguese often leaves the possessive unstated when it is obvious from context.

So:

• o agregado familiar mudou o orçamento

naturally implies:

• the household changed its budget

Adding a possessive is possible:

• mudou o seu orçamento

But it is often unnecessary, and sometimes less elegant, if the relationship is already clear.

Portuguese frequently prefers the simpler version.

In Portugal, this expression is very common in official and practical contexts. Learners often meet it in things like:

• tax documents
• school forms
• housing applications
• social support documents
• personal finance discussions

It usually refers to the group of people who live together and function as one financial/domestic unit.

So although the literal parts are:

• agregado = aggregate/grouping
• familiar = family-related

the real-life meaning is best understood as:

• household
• family unit

A broad European Portuguese pronunciation would sound roughly like this:

• Depois du imprevishtu, u agregadu familiár mudou u orçaméntu.

A few useful points:

• do often sounds close to du
• unstressed o often sounds like u
• depois in European Portuguese is typically closer to dsh-poish than a fully open English-style deh-poys
• imprevisto often has a sh-like sound in -isto in European Portuguese pronunciation
• orçamento has stress on men: or-ça-MEN-to

This is only an approximate guide using English spelling, but it can help you hear the European Portuguese rhythm better.

It sounds neutral to somewhat formal.

The main reason is o agregado familiar, which is more formal and administrative than everyday a família.

So:

• Depois do imprevisto, a família mudou o orçamento.
  sounds more everyday

• Depois do imprevisto, o agregado familiar mudou o orçamento.
  sounds more formal, practical, or institutional

The rest of the sentence is straightforward and natural.