In teenstelling met registrasienommers verander onderstelnommers nie.

It means in contrast to, unlike, or as opposed to.

So:

• in teenstelling met registrasienommers
  = in contrast to registration numbers / unlike registration numbers

This is a fixed expression in Afrikaans. The met is part of that expression, so learners should treat in teenstelling met as one chunk.

Because Afrikaans main clauses normally follow the verb-second rule.

In this sentence, the first element is the whole phrase:

• In teenstelling met registrasienommers

Once that phrase is moved to the front, the finite verb must come next:

• verander

and only after that comes the subject:

• onderstelnommers

So the structure is:

• In teenstelling met registrasienommers
  • verander
    • onderstelnommers
      • nie

If you strip away the fronted contrast phrase, the basic clause is:

• Onderstelnommers verander nie.

Afrikaans often uses a two-part negative pattern, but in short sentences like this, you may only see one nie because it is already in the final position.

Here the sentence ends with:

• ... verander onderstelnommers nie.

That final nie is enough.

Compare:

• Onderstelnommers verander nie.
• Onderstelnommers verander nie maklik nie.

In the second example, there is extra material after the first negative position, so you get a final nie as well.

So the short answer is: the negation is sentence-final here, so only one visible nie appears.

Because the sentence is making a general statement, not talking about specific numbers.

Afrikaans often leaves out the article when speaking about things in general, especially plural nouns:

• registrasienommers = registration numbers in general
• onderstelnommers = chassis numbers in general

If you added die, it would usually sound like you mean particular ones already known from the context:

• In teenstelling met die registrasienommers verander die onderstelnommers nie.

That would mean the registration numbers and the chassis numbers, not numbers in general.

They are compound nouns, which are very common in Afrikaans.

They break down like this:

• registrasienommers = registrasie
  • nommers
• onderstelnommers = onderstel
  • nommers

Afrikaans usually writes compounds as one word, whereas English often writes them as separate words:

• Afrikaans: registrasienommer
• English: registration number

The last part, nommer / nommers, tells you what kind of thing it is: a type of number.

In vehicle-related language, onderstel means chassis, frame, or undercarriage.

So onderstelnommer is a chassis number. In some contexts, this may correspond to what English speakers call a VIN, though the exact usage can depend on context.

It is active and intransitive here.

So:

• onderstelnommers verander nie means
• chassis numbers do not change

It does not mean are not changed by someone.

If you wanted a passive idea, Afrikaans would normally use a different structure, for example:

• Onderstelnommers word nie verander nie. = Chassis numbers are not changed.

So in your sentence, verander simply means change.

Yes. Even though both words are plural, the sentence is making a general rule about two categories:

• registration numbers
• chassis numbers

English does this too:

• Registration numbers change, but chassis numbers do not.

Afrikaans often uses the plural in this kind of general statement. So the sentence is not about one specific number, but about how those kinds of numbers behave in general.

Yes. The basic statement is:

• Onderstelnommers verander nie.

The original sentence puts the contrast first:

• In teenstelling met registrasienommers verander onderstelnommers nie.

This fronting gives extra emphasis to the contrast. So the meaning stays the same, but the original wording highlights the difference right away.