Se cambi il verbo, cambia anche il senso del sostantivo che lo segue.

Because Italian often uses the present indicative for real, general, or likely conditions.

So:

• Se cambi il verbo = If you change the verb
• cambia anche il senso... = the meaning also changes...

This is a very common pattern for general truths:

• Se studi, impari. = If you study, you learn.
• Se mangi troppo, stai male. = If you eat too much, you feel sick.

Italian does not need will here the way English sometimes does. You normally do not say Se cambi il verbo, cambierà... unless you specifically want a future meaning.

They are both forms of cambiare, but they have different subjects.

• cambi = you change
  The subject is an implied tu
• cambia = it changes
  The subject is il senso

So the sentence is structured like this:

• (tu) cambi il verbo
• il senso ... cambia

Italian often leaves subject pronouns out because the verb ending already shows who the subject is.

In Italian, articles are used much more often than in English, especially when speaking about things in a general sense.

So Italian says:

• il verbo
• il senso
• il sostantivo

where English might simply say:

• the verb
• the meaning
• the noun

or sometimes even leave the article out in a more abstract explanation.

This is very normal in Italian grammar explanations.

Del is the contraction of di + il.

• di = of
• il = the
• del = of the

So:

• il senso del sostantivo = the meaning of the noun

This kind of contraction is extremely common in Italian:

• di + il = del
• di + lo = dello
• di + la = della
• di + i = dei
• di + gli = degli
• di + le = delle

Anche means also, too, or as well.

In this sentence:

• cambia anche il senso...

it means that not only does the verb change, but the meaning changes too.

Its position is natural and idiomatic. Italian often places anche before the word or idea it is adding emphasis to. Here it highlights that the meaning also changes.

A natural English translation would be:

• If you change the verb, the meaning of the noun that follows it changes too.

Literally, it means:

• che = that / which
• lo = it
• segue = follows

So:

• il sostantivo che lo segue = the noun that follows it

Here, che introduces a relative clause describing il sostantivo.

The clause is:

• che lo segue = that follows it

This tells you which noun we mean: the noun that comes after the verb.

Lo is a direct object pronoun meaning him/it for a masculine singular noun.

Here it refers back to il verbo, which is masculine singular:

• il verbo → lo

So:

• il sostantivo che lo segue
  = the noun that follows it = the noun follows the verb

Why not gli? Because gli usually means to him or to them, so it would not fit here.

Why not nothing? Because seguire here needs an object: the noun follows something, namely the verb.

Not with exactly the same meaning.

• che lo segue = that follows it
• che segue can sound like that follows / that comes next, without clearly stating what it follows

In this sentence, lo is useful because it clearly points back to il verbo.

So:

• il sostantivo che lo segue = the noun that follows the verb

Without lo, the meaning becomes less precise.

Because Italian normally drops subject pronouns when they are not needed.

The verb endings already tell you the subject:

• cambi = you change
• cambia = he/she/it changes

So Italian prefers:

• Se cambi il verbo, cambia anche il senso...

rather than:

• Se tu cambi il verbo, esso cambia anche...

Adding the pronouns would usually sound unnecessary unless you want special emphasis or contrast.

Italian word order is flexible. Both of these are possible:

• cambia anche il senso del sostantivo...
• anche il senso del sostantivo... cambia

The version in your sentence sounds very natural because Italian often puts the verb before the subject, especially when introducing the result or focusing on the action.

So:

• cambia anche il senso...
  feels smooth and idiomatic in an explanatory sentence.

English is usually more rigid, but Italian allows this kind of variation much more easily.

Both can be used, but they are not identical in tone.

• sostantivo = the precise grammatical term noun
• nome = literally name, but it is also often used in school grammar to mean noun

In a grammar explanation, sostantivo sounds more exact and technical.

So in this sentence, sostantivo is a good choice because the sentence is talking about grammar very explicitly.